Multiple topics; RPMS? Engine braking?

[BigBlockBurby]

My trucks a 1993 Chevy C3500 Crew Cab Dually, running the TBI 454 with a 4L80e behind her. Just rolled over 100k last night on the way to work. Heres the deal. Cruising at 65 MPH, my RPMS are crisp at 2500. Not something Im happy with in this truck. Truck is on 265 75 R16 BFG All-Terrains. A little wide, causing the duals to rub, but my spacers are being shipped as we speak. Otherwise, truck is 100% stock. Tires arent tall, So I cannot imagine why my RPM's are so high. My old crew cab had a Vortec 454, on 35's, and at 65 She was a nice smooth 1950 RPM's, give or take. My question is, what is my issue here? Im told the Dually has 4.10's out back, which is what my work truck had, so why is my RPM's up so high?

There HAS been some recent trans work, new shift solenoids, speed sensors, TCC solenoid, etc etc. Don't know if that helps, but my other issue. At 65 MPH, Ill let off the gas as I coast down a hill, and I get engine braking, in OD. This is something I hate, I don't need engine braking in OD, I wouldnt be towing anything in 4th gear, so why is there engine braking? It was not doing this prior in OD or 3rd gear. Then I put the new parts, and now Im getting it in all gears. Does this have something to do with my RPM's being kinda high? I've driven other trucks of the same build, and I KNOW I should be closer down by 2000 RPM's. Trans shop trying to tell me my trans needs a rebuild, but I know for a fact it doesnt. Engine shop said My gears might need to be changed, which I am not up for doing, If I gear the truck, it'll be after my Straight axle 4x4 conversion up front and my cummin's, in which case I'll gear it appropriately for my Turbo Diesel and my 35's.

At 60-70MPH, my truck shakes violently on cement freeway portions, as if my truck would be dancing on the highway.

Any advice here guys? Truck has no codes. Runs strong, tows my camper like a monster, 2800 RPMS towing up hill. I could use your great knowledge guys

PS; Not sure if I'm getting lock-up. Think It could be stuck locked or unlocked?

[ChevyTech]

This vehicle needs to be driven with a scan tool on it, by somebody experienced with the scan tool.

If the computer is sending a command that does not take place, then trouble codes should be getting set.

My guess is there is a problem that is affecting what the computer wants the transmission to do.