Truck Repair: 700 R 4 auto transmission, vacuum modulator, manifold vacuum

Question
I  have a 1987chevrolet siverado with the 700 R4 auto transmission.  The transmission will not shift to second or third gear.  I replaced the tranny with a good one.  It still will not shift could it be the computer?  I was told if i put a older distributer on it, it would run without the computer and shift fine.  any suggestions  

Answer
Hello Denny,
An 87?...I don't think any computer is involved.
I believe it has a vacuum modulator on the right hand side of the tranny, just above the pan. A vacuum hose connects from it to the intake manifold. Full manifold vacuum is needed, or it won't shift.
You also need to check the modulator to see if the diaphragm in it is leaking. Connect a piece of vacuum hose to the modulator and suck on the hose. It should hold vacuum.

If you don't have the vacuum modulator, then you will have a throttle valve, which is near the dipstick tube in the tranny, and runs a cable to the carburetor. Sometimes those valves will stick, and pulling some pressure on the cable at the carb, and then releasing it quickly will pop it loose usually.

Van