You should be good at 4" drop if you cut down or remove the bump stop. They produced over 10 million GMT-800 trucks they aint that special... cut that frame if needed, you'll sleep fine at night.

 

I had a 2wd ext cab and did a 2/4 drop, cut down the bump stops and still hit them on any decent bumps in the road. In my (limited) experience if you're going to do a 2/4 you should do a mini c-notch (don't know if that's the proper term). When I put in mine I researched it and found most people saying it wasn't needed, and you could get away with not putting it in. But I think it's a better ride with it. I don't ever want to hit the frame, but that's just me.

 

I have a 01 with a McGaughys 2/4. I removed rear bump stop after hitting it every now and then. I’ve only barely tapped axle to frame once or twice since. I plan to put a short ES bump stop in just to stop the bang on that rare occasion. It’s going to take helper bags to be able to drag a trailer though.