If you're running 4.11, you're in the ballpark:
Checked and sure enough it has 3.55s so that means it is a transmission issue.
It would seem at that speed and RPM the trans is in 3rd a 1:1 ratio, and the rear gear ratio is around 3:55.
The specific rpm is based on tire size and accuracy of the Tach.
My 02 with 3:55 will run about 3000 rpm at 70 mph 'out' of OD.
There is nearly a 1000 rpm difference between OD and 3rd.
Upshifting to OD then drops the RPM back to about 2100.
My speedo in known to be about 2 mph fast.
In between this is the converter lock which is a difference of about 300 rpm on to off.
You can still be in OD but the converter can be either locked or unlocked depending on how much light throttle is applied and the load on the motor.
It's all a matter of throttle angle as determined by the TPS sensor, VSS and motor RPM.
From these values the PCM makes the decision as to what to do with trans gearing control with a little timing delay thrown to prevent hunting, as applied to an electric controlled trans.
Older throttle control and govenor shifting is done differently to arrive at the same results such as the old AOD trans or even earlier the C4 and C6 types that were total vac and govenor control to arrive at about the same results.
The OD switch only signals the PCM for the intent then the PCM passes the action to the trans.
I don't know what you got going there but it 'ain't' right if it's happening at very low speeds.
Nice when you buy someone else's troubles thinking you get a bargin. That's why they sold it.
Turns out that even if something is obtained free it 'ain't' free after you get it and have to fix it..
I'm gonna be honest, I can't make much sense of what you are saying. I'm trying, but I don't speak transmission I guess.
Seeing that the gears are 3.55s, overdrive isn't working right at highway speeds. Or at least that is what I am assuming based on what you said. So, with all the different things you mentioned, where do you think I should look to figure this out? Could the transmission being overfull cause this? Or is this more likely to be an electrical issue? Or mechanical? I'm more confused now than I was in the beginning.
*Edit* Another note about the transmission issue. On the highway when cruising at 65mph with overdrive on, while it is running 2800, if I let off the throttle, the rpms drop to about 700.
In all honesty, I bought a $550 motorcycle that needed a little work and traded it for this truck. So i'd say overall I'm still not doing too bad. I always expect used stuff to need some work.
My other project today was trying to figure out what is going on with the A/C. It was retrofitted to r134a, but the compressor isn't kicking on, and I can't find any obvious leaks. I tried pulling a vacuum, but had no luck. Couldn't get it to pull anything at all. But between the noise the vacuum pump and my compressor make, I couldn't hear where it might have been leaking. So, I decided to buy a can of r134a with leak detector in it to see if I could get the compressor to kick on long enough to get the dye through the system to see anything. So I hook it up to the gauges and start adding the can, pressure is increasing like normal, then all of a sudden, nothing. No pressure, no hissing, NOTHING. Again, no obvious signs of leakage. So, I decided I'd jumper the ac clutch for a couple seconds to try and pull some dye through the system. When I did, the system pulled almost 20inHg of vacuum instantly. I didn't want the compressor to burn up, so I didn't do it for long. I'm sort of at a loss at what to do now. Also, Any suggestions?
*Edit* I forgot to mention that when I was charging the A/C, I never read ANY pressure on the high side. Nothing at all.