Transmission shifting problems

[55Nick15]

Hello! I am new here but have been a lurker for a long while. I drive a 2003 4x4 ls blazer that I am getting ready to add a lift and stuff on. Before I do that tho, I want to line out a problem that started about a month ago.

4x4 with 373 gears. Do not have G80 and I have never done a transmission fluid flush.

my problem is when Im driving at highway speed, 45-70 mph, and I start going up a hill.. the hill can be steep or not steep at all just a gradual grade, my transmission wants to downshift to third and then go back to fourth. This happens continuously and constantly as in i can watch the tach go up and down every 1-2 seconds. It will stop if I let off the throttle or hammer down to get it to stay in third. Super annoying and I dont want to add bigger tires with this happening thinking it may compound the problem.

I saw where the TransGo shift kit might help this but Id have to have it installed by someone because trans work is the only thing I wont tear into myself, everything else I can handle.

Any input would be helpful because I need to get this sorted out.

Thanks!

[Anthony Hernandez]

Sounds like your feathering the pedal to me.

[55Nick15]

It wouldn't be feathering if it does this in cruise control also. Car never did this prior to last month with 185k miles. Did not change my driving habits since last month nor did my girlfriend.

[HawkeyeC25]

Sounds like it could be the TCC unlocking and reapplying. When it feels like it shifts to 3rd on it's own, drop the shifter into 3rd and see if you feel a shift or if it just feels like it stays in 3rd and nothing happens. If you feel a shift, it's probably the TCC that's unlocking. If you feel no change, it at least confirms it's truly going into 3rd. Next would be to figure out if it's commanding 3rd or slipping the 2-4 Band.