Ok so let's hammer out basic auto trans diag...some of the most basic things you can do which have not been reported on yet is checking fluid level and condition. If not correct, remedy the situation before going any farther. If they appear ok, suggest investing in a new filter and some new Dexron III anyways. It's a whopping 4-5 quarts, if you can't afford it you can't afford to drive a car. If that doesn't solve the problems, you need to do some basic fluid pressure checks. This will require an oil pressure gauge (higher than engine oil pressures, typically a 250 or 300 psi gauge set) and some TH400 know how. Use the TM's or Al Gore's interweb. First thing you need to check is line pressure. If the pump is not putting out pressure then nothing works. Next you should be checking throttle/modulator and governor pressure. If these are OK then you go on to the clutches/brakes. These older non-electronic transmissions are very basic in nature and easy to diagnose even if you have no idea what is going on with the automagic mystery. Then and only then if it has failed to this point should you be pulling the trans for a rebuild. After all it may just need fluid, cooler, filter, or pump.
I personally like the people that come on here and ask for help diagnosing a trans problem and then say they are going to rebuild it. If you can't diag it you shouldn't rebuild it. Leave it to the pros.
I hope this steers you in the right direction and give others some insight on how to handle transmission issues.
Cheers