I just rebuilt a big block 727.
Lots of good new parts, billet internals, manual valve body with low band apply, 4500 stall converter

Just did the initial start and check to see if the wheels move when put into respective gear.
Reverse works
Neutral has slight forward movement but I can stop the wheels by hand.
Low and other gears seems to go as they should-

This is on Jack stands


When I put it in reverse from being in gear it stays as forward. If I shift it to reverse from park is goes in reverse. Has done this several times- i checked and re adjusted the shift linkage and that is correct.

Why would reverse be forward only if shifting from forward gears??????
Shifted to reverse from park it is reverse!?!?!??

Thoughts?

Put it on the ground and see how it works that way
I'm thinking new tight bands and clutches may be dragging making it move that way

It sounds like the manual valve is not moving to the correct position to block the desired ports. Sloppy linkage would be my bet. Disconnect the linkage at the trans. Shift the lever by hand. My bet is that it'll act normal. If not it's possible that the lever that fits into the manual valve (internally at the valve body itself) is slightly bent and out of alignment not locating the manual valve correctly in each gear.
Doug

I am hoping it’s a valve body issue and that just needs a fix and not have to remove and disassemble the trans….

I took it for a quick drive, and geeez it feels so much faster with an an
To than it did with the 4 speed.

Still does the reverse thing.
I tried to see if I could shift it into reverse from any point after going forward, just slowly moving the shifter towards reverse- no luck. It is either forwards or neutral then park. I readjusted the linkage per the hurst instructions and same- no change.

I’ll call cope on Tuesday and see what he thinks may be going on.

Jack it up so you can worked on it underneath and the drain and remove the tranny pan and verify the shift linkage inside the case is moving the manual valve correctly on the valve body and not making the manual valve stuck between two gears
Have some one shift the shifter in the car and you verify that when you remove the pin from the shifter linkage inside the tranny off of the valve body linkage that the shifter linkages doesn't move at all, the pin should move freely up and out and in and out as well as drop back into that hole with no movement on the valve body linkage at all, NONE
If it does move adjust the shifter linkage from the shifter until it doesn't move the interior linkage at all when sliding it in and out of the tranny linkage

I have comments on several transmission problem on this forum, and can't say it enough if you have a transmission problem before you drain the pan or pull it out, hook up a transmission gauge and check the pressures, Torqueflites have several test ports and you can get clues to what is going on, clues that can be very helpful, if you have to take it back apart. You can buy gauges reasonable at harbor freight. Read the service manual on what pressures to expect. If you have a race valvebody you need to call the company and they can give you the test pressures that are normal for your valvebody. I have worked on automatic transmissions since 1975, a pressure test can save so much time on those weird problems.

on top of Dougs coment, check each detent oosition to make sure your linkage arm is the right length.

Sounds like the linkage is loose on top of the trans.