4L80E 4th grear slipping

[7.4Burb]

I have a 96 K2500 Suburban with 454 and 4L80E with 134k miles. Have owned the beast for 15 years and have done all normal maintenance on it. Had the transmission rebuilt about 17k miles ago because it lost 1st and 3rd gears. Now just this week it has started slipping really bad in OD 4th gear. Checked fluid, good was a it low though. Truck pulls hard 1st, 2nd and 3rd. and will run in 4th but every once in a while like a slight grade it will slip and rev about 800 rpm in 4th and if I feather the gas it will catch and be normal for next 5 miles or so until it does it again. A few times it felt like it dropped all the way to 2nd and then back to 3rd. any ideas? Torque converter going, 4th gear clutches shot??