I've noticed this slightly before, but the past few days it seems worse. Around 45 mph it feels like the Hummer starts to buck a little. There's a little bit of a bog when I accelerate slightly and then the bucking. If I stick my foot in it and get it up past 50 then it feels like it goes away. I put it in neutral while doing 45 and did not feel the bucking/bogging, so I'm assuming it's not a tire balance issue. Any ideas?

 

Yeah..I think I have a guess..at thet speed, the tranny is trying to decide 3rd or 4th gear and it it hunts back and forth..put your gear selector in 3rd and see if it still happens..otherwise I think it's normal..

The PCM tune will fix that hunting around.

 

I think that might be it. It's like it can't make its mind as to which gear it wants. Now I'm going to search for the PCM tune.