only when the a/c is on !

I picked up a used t-100 a few months ago for less money than it would cost me to fix the a/c in one of my GMC suburbans ( $1,000) even though it had 180,000 miles on it, it was well cared for and ran perfectly. The a/c blew at an amazing 40 degrees ! Last night, on my way home from work...I was sitting at a light in drive gear with the a/c running...suddenly, the entire truck began to shake and felt like it was going to die. I turned off the a/c and tried to use the gas pedal to bring it back to life. I got home ok (did not use a/c again). But now, there feels like a skip in the engine while idling even with a/c off. I am wondering where to start checking ?? Plugs, coils...I am assuming that it is electrical in nature...but am not sure. Any help would be much appreciated. If it was my GMC, I would be confident that I would be able to isolate the problem. This engine reminds me of my outboard on my boat...with the individual coils etc. Thank you in advance...

artie in miami ( I need that a/c back fast !!)