hey whats up

i have a 2004 chevy silverado ext cab i recently had the trans rebuilt @ 121k miles... now since this has been done ill be driving around city streets noticing that the rpms increase/decrease when @ 45mph (this also happens on the fwy) it seems that the tranny is trying to shift gears when its not needed. ive tried google and came up with no results and would like some more insight before i take it in to get this checked... also when i turn on the towing overdrive switch it seems to not do it as much but still there

any info would be greatly appreciated...

 

sounds like the TC is locking/unlocking. at about 40-45mph lite throttle is sounds about right. when you use the tow/haul it will keep your TC from locking up