Check u joints, then check rear pinion flange make sure your pinion nut hasn't backed off. If it's ext cab make sire your center bearing isn't bad. Does it act like it could possibly be a fuel supply problem? That could explain whey you'd be surging under load.
U joints are all good. It doesn't act like its a fuel supply issue but im not ready to rule it out. It feels more mechanical and very consistent. It didn't seem to get much better or worse trying different driving techniques however it is less noticeable at lower rpm. Just for shits and giggles I shifted into low 4.7 high 2.28 in 2wd and its still noticeable with the t case in low range no foot on the gas but not nearly as bad as when im driving down the street. Need to check the pinion nut tomorrow.
When it first happened I was driving and everything was fine, stopped at a light and when i took off I noticed the problem which existed entire drive home and hasn't stopped so it feels like something has broken or became loose. Trans needs a rebuild it would be nice if that would fix the problem.
