C4 slipping at cruise

[Chiclassics]

Hey guys

So my 74 with C4, was installed 6 months ago. The shop cleaned it up(typical transmission service) and installed. The C4 should be all stock. When I drive no noises shifts good etc. However when I drive on freeway , at cruise ~65mph, my RPMs are at 3000-3200 it slips/looses grip momentarily(no RPM raises per se) until I slow a little and it feels it grips again. The same scenario occurs when i hit slight slopes like 10-30degrees and when the RPMS are at 2200-2400. So it looks like whenever there is a certain load happening on car - 2800/3200 rpm at cruise flat fwy or 2200-2400 slight elevation the C4 is losing grip almost like hunting for gear and no noises.

Is it my torque converter or C4 bands themselves ? or is it simple vacuum modulator adjustment? I did already adjust my vacuum modulator 2 turns in.

Appreciate insights before i give it to rebuild.

 

[Broncobowsher]

My first check, you didn't mention, fluid level.
Second thought, they put the wrong transmission filter in. Someone will step in with all the details, but the Bronco pan has a deeper sump than the car transmission. Has a shorter filter.

I can tell you it is NOT the bands. The bands are not used in 3rd gear. Only 2nd gear, reveres, and when manually selecting 1st gear.

 

[Chiclassics]

My first check, you didn't mention, fluid level.

Hi @Broncobowsher ya fluid level is good, I made sure its up to the mark when hot.

I can tell you it is NOT the bands

Great to hear this.

Second thought, they put the wrong transmission filter in

I had a hunch . the guys worked on installing this transmission are not "expert" ford guys. they were someone in proximity of the bodyshop. So when they did service they could have changed the filter as a part of service and put wrong one in. Because my symptoms are subtle and sneaky . And sometimes it feels gears are shifting too quick and slight burning smells with no excess revs or loads.

Let me talk to my guy to see if they can change filter

 

[SLOWnEASY]

If I remember correctly if you have a Bronco C4 pan filled transmission there should be a bump in the bottom of the pan and inside the pan should be a pickup tube. That tube goes from the filter and down into the bump. Maybe that tube slipped and dropped out of the filter.