My Tahoe seems to "hunt" for a gear at certain speeds. About 40 and 60 mph with steady throttle and level ground. It's weird, like maybe the converter is trying to lock causing the truck to very slightly buck intermittently unless you speed up or slow down. 3 mph up or down and it goes away.
Any ideas?
If it's a 4L60e transmission, it's a factory defect problem. Something to do with the bores in the valve body wearing out and not holding pressure.
You can buy a "fix it kit" on ebay for around $40 and requires pulling the valve body and tearing it down to re-drill the bores with oversize seals.
My 2000 S-10 done the exact thing your describing, I bought a used valve body off ebay from a transmission vendor that guarantees these to work. He cleans and checks them. It cost me less than $100 and 8 hours of my time to replace.....my car shifts and runs like it did the day I bought it.
Dealers charge upwards of $350 - 400 to do this repair..
Do a search for "code 1870" on google and you'll see what I'm talking about. Sometimes it will throw a check engine light...sometimes it won't.