Re: transmission shiftiness
How tired is the motor? If it's got a lot of blowby then it could be a matter of insufficient vaccum to properly operate the modulator. I'd do a compression test just to be sure. If it passes that then the motor is probably okay. The reading isn't as important as the difference between cylinders. More than 10% isn't a good sign. If you get one that's a little low try squirting some gear oil into the cylinder and re-testing. If it gets better the problem is the rings. If it doesn't then it's the valves. If the rings are good you can just send the heads out for a valve job and new seals. Then your motor will be back up to snuff.
Typically if the governor gear fails it shreds apart and the trans just won't shift at all. Though don't overrule this either. It's simple to pop the cover off and take a look. Have a new cover handy though,because if it's a pressed on cover the factory uses locktite to hold the cover into the case, and it is usually damaged during removal. I can't remember if TH400s use this style cover. All 700R4s and TH350s do.
If it slips then the porblem is inside the trans, and a rebuild is the only way to correct it. I find this unlikely though, the TH400 is a really tough trans, even stock. I've seen fleet vehicles go through two or three engines in front of a stock, regularly serviced TH400, even when the trucks were used to plow snow and tow trailers over the limit of the truck.
