1999 bravada engine stutter with a/c on

I got a 99 bravada and when truck is in gear and I turn the a/c on it runs real rough. The rpms fluctuate and it is almost like it wants to stall is the best way to put it, (but it DOES NOT stall.) Any ideas?

How long since the last tune-up? Sounds like a misfire, is the Check Engine light on?

I bought the truck in may and have not done a tune-up. It runs great when a/c is off and it only does what is descrided above when a/c is on and truck is at idle.

You might check and see if any of the spark plug wires are worn or burnt. It sounds like an ignition problem.
At idle with the AC on, the motor must not only idle up to keep the engine speed at 700 rpm, it must do it without increasing the exhaust emissions.