One problem related to radiator has been reported for the 2003 GMC Envoy. The most recently reported issues are listed below.
2 complaints noticed enginee running hot, added fluid to radiator, near empty. A couple of months later, same thing. 3 months later, during oil change, mechanic indicated while doing checks that the radiator fluid was low. Told him this was the third time, he added fluid, pressure checked radiator - no holes or leaks. Seems to be evaporating. Air conditioner blowing hot air (excluding the fact the panel with ac controls quick working a loooonng time ago). Took in to dealer for repair. After $600 and all day visit with dealer, the piece broken was the size of a 2"-4" block of plastic. This little piece just quick working, it was referred as a control switch of some sort under the dash board. Sounded kinda hokey to me - I can imagine a compressor going out and you do not have cold air - the name of it escapes me - but the mechanic did indicate there was some sort of technical report out there on it as well. Just found out from husband the name of the piece - the actuator door quit.