Truck vibrates

I have a 2003 silverado that I recently did an engine swap from a 4.3 V6 to a 2005 5.3V8. Whenever I stop at a light the truck seems to vibrate alot when the A/C is on. I turn it off and the vibrating stops. Please help. Vibration is really getting to me.

Maybe an engine mount is gone. Or perhaps a sign of the A/C Compressor wearing out. Or maybe your computer needs to know the A/C is on and it's not getting the correct signal. Perhaps the engine needs to throttle up a bit when the Compressor comes on...

Just some thoughts...

Where are the engine mounts? I really do not know that much about engines .thanks

So who did the swap? Look for the ac compressor properly mounted.

A friend of mine did the swap. How do I know if its mounted properly. The truck was fine but then i went to my ranch and the road has a bunch of bumps,and holes, then thats when it started.