Were death camps originally intended as death camps and if not, what changed?

Dachau concentration camp was set up in 1933 to imprison political opponents of the Nazi regime, mainly communists. Non-communist Jews began to be sent there in 1938. Unlike Auschwitz, it was never a “death camp” in the strict sense of the word, but of course lots of prisoners died there.

Both may well be true. It also depends on your definition of "death camp".
While some camps were designed and built from the outset as extermination camps, and these had very little in the way of other facilities except some barracks for the workers, most were designed and built as prison facilities, work camps, and temporary holding facilities for prisoners intended for transfer elsewhere.

As to gas chambers being originally intended for fumigating lice infested clothing, this is possible but somewhat unlikely given the scale of the operations. For that purpose a smaller facility will suffice.

Most fixed installations to which persecuted peoples were taken and in which they were murdered were built originally as work or concentration camps. Auschwitz, which gained notoriety for its having had the largest number of gas chamber victims throughout the war, was built on the site of a military barracks and originally for purposes of concentration only. Most of the people murdered at Auschwitz were murdered there in the final stages of the war.

While this is the case for most fixed installations, there were three that were purpose-built for murder, and all three were in the General Government of occupied Poland: Belzec, Sobibor and Treblinka. These three camps were part of what is known as Operation Reinhard, and were constructed with the intention of their being the place in which the entire Jewish population of the General Government would be eradicated.

Belzec started operating in March of 1942. Until its eradication in the summer of 1943, it may have been responsible for as many as 600,000 murders. Only two people are known to have survived Belzec, one of whom was murdered in Poland in 1946.

Modeled on Belzec, Sobibor began operating in April of 1942. Until its eradication at the end of 1943, Sobibor is thought to have been the site of some 160,000 murders. There were several escapees, most of whom broke out after the uprising of 1943.

The largest and most efficient of these three purpose-built camps was Treblinka. From its commencement as a death camp in April of 1942 until the end of 1943, Treblinka was the site of approximately 900,000 murders. There were several survivors and escapees, partly as a result of the uprising in 1943 and partly as a result of the chaos that ensued in the earlier period when the camp was understaffed and overpacked with arrivals from Warsaw and its environs.

All told, these three camps were responsible for the murder of most of the Jews living within occupied Poland, and were constructed for that express reason. As a result of these forays into fixed killing installations, gas chambers were added at other camps as well, like Majdanek and Birkenau, and even at the site of labour camps (like Mautthausen, for example).

Note that gas had been used even prior to the construction of these sites - particularly in terms of mobile gas vans, such as operated in Chelmno and in Minsk, but also as fixed installations. Gas chambers had been employed, for example, as part of the T4 program, by which large numbers of people with disabilities were also murdered. By the end of the war, it is estimated that some 300,000 people had been murdered as part of the T4 program exclusively.

Most Nazi concentration camps were not death camps. The Nazis ran dozens and dozens of camps, but only 4 of the camps (Chelmno, Treblinka, Sobibor and Belzec) were intended solely for extermination purposes. All 4 existed in a state of extreme isolation and secrecy during the war. The work camp at Majdanek was converted to an extermination camp late in the war. Birkenau, the sister camp of Auschwitz, was also converted to a extermination facility during the war. The million estimated to have been exterminated at "Auschwitz" were actually killed in the Birkenau facility which adjoined Auschwitz proper.

The first inkling of this was that in November of 1942 the Polish government in exile in London published a report that announced that the Nazis were systematically exterminating Jews as part of program that had been begun early that year (1942) and was being run by Himmler. This report identified Treblinka, Sobibor and Belzec as the death camps being used.

The great majority of camps were either camps for political prisoners (like Dachau) or were work camps, intended to contain and enslave the enemies of the Reich. At the end of the war most of the occupants of these camps died either from starvation, as the Nazis lost the ability to provide food to the camps, or from cholera due to lack of fresh water. Water is carried by pipes that go over bridges. When a bridge is destroyed, the water supply to an entire area is turned off. So, in a sense, all the camps turned into death camps in the spring of 1945, even though most of them had not been designed for that purpose.

The policies against the Jews developed gradually. The Wikipedia article on Holocaust gives a rather complete history. Complete extermination was decided at the Wannsee conference in 1942. Many camps had a dual purpose, they were both labor camps and extermination camps, like the best-known of them in Auschwitz-Birkenau.

It is indeed hard to tell with certainty what they were thinking or planning in 1933 or earlier. (Plans and intentions are usually not documented). Deportation of Jews out of Europe was apparently also considered. In 1942 deportation was not an option, and they were loosing the war. So they decided to kill all Jews on the territories that they still controlled. Most of the killing was done in the last two years of the war.

I did not understand your speculation about "out of resources" and how is this related to the matter. The operation of mass extermination actually consumed many resources, including trains and troops which could otherwise be used for the war effort. So the operation was conducted despite the scarcity of resources, not "because" of it.