03 1500 4x4 5.7
Mods - fat bob's garage 3'' and 33's
65,000 miles

Truck doesn't seem to like 4th gear in any situation.
On light to heavy acceleration shifts to third fine then holds third for a little too long eventually shifts to 4th then immediately shifts to 5th.
Climbing a hill while in 5th gear tranny ALWAYS down shifts to 3rd
While in 5th turning O/D off tranny shifts to 3rd like 4th doesn't exist
Between 40mph and 50mph tranny might shift out of o/d if I let up on the gas sometimes
Same symptoms in 2WD or 4WD

After doing some research I checked the fluid, level was good seemed nice and clean. Decided to flush the tranny anyway and change both filters then replace with new fluid. Fluid level is correct after change also.

No CEL or any other codes

Culprits; shift solenoid, PCM, TCM? Maybe but why no codes?

Any help would be greatly appreciated. There's not too many reputable mechanics around my small town in Alaska and the dealership is the devil.

 

I would get a scanner that can read data from the transmission, Like a DRB3 and watch the gears as you are driving. This will show you if you are going thru all the gears. If you are missing 4th gear, then I would remove the pan and inspect the side plate on the valve body.