I have a 1983 Chevy Van Motorhome, which I guess hardly qualifies as a hot rod. Still hoping to find some knowledgeable people here to give some advice.
The vehicle has a 6.2 non-turbo diesel engine. The original transmission was a TH400, which I replaced with a rebuilt, beefed-up (700hp) 700R4 from what I thought was a reputable transmission shop. It has a lock up torque converter.
I talked to the shop about my problems but didn't like very much what they told me. So I'm trying to get a few more opinions here.

Here are the issues I have.

1. The transmission shifts fine and performs nicely and quiet up to 3rd gear. In overdrive it emits a slight howling noise, most pronounced around 60 - 65 mph. If I engage the lock up the howling gets much worse to the point where you want to disengage it right away. If I keep it locked and go faster it quiets down somewhat but the noise is still there and it simply shouldn't be with a new tranny.
There is absolutely no noise in 3rd gear, with and without lockup.
The front part of the drive shaft had to be shortened. I had this work done by a professional drive shaft shop. My first suspicion was that the drive shaft was out of balance but the people who shortened it assured me they balanced it.
The drive shaft has all new u-joints and a new center bearing.
Has anyone any ideas on where the noise comes from?

Note: here is what the transmission shop told me. My lockup solenoid gets 12V from a separate brake pedal switch to allow disengaging of the lockup when braking. The ground wire runs to a dash board switch and then to ground. They think there is a bad or insufficient ground for the lockup solenoid. They think I should ground it right on the tranny and put my dash switch in the hot line.
I'm having a hard time believing that's the problem but I might be wrong.

2. I also have a temperature problem. When cruising on the highway at around 55 mph the fluid goes to about 230F, around 70 mph it is up to about 250F. This is without the converter locked due to the howling problem mentioned above.
The transmission shop people said it was not a problem to drive the 700R4 without lockup, but I have read other statements just to the contrary. I'm not using the radiator integrated oil cooler but a 20,000 lbs GVW rated stacked plate cooler in front of the radiator.
Now my temperature problem is probably related to not using the lockup. I'm still surprised that the transmission generates that much heat.

I'm not sure if I mentioned everything that is important. If something's missing let me know. I would really appreciate your input.