Hello and thanks for using Just Answer my name is XXXXX XXXXX I would like to help you with this question.Without knowing what your diagnostic codes are all i can do is suggest what I would check first. You have a good reverse but no forward range from neutral 1)First is to make sure the linkage adjustment is dead on "Because in forward the C-1 clutch is fed directly through the selector shaft connected to the linkage. 2) second I would take a good look at the Pressure switch on the valve body,It will be bolted to the bottom of the valve body,and there will be a transfer tube that has a bracket bolted over it, colors can be black"Old style" or Blue "New style. The o-ring for the reverse part of the switch has a nasty habit of popping out of its groove. Also the valve body E shift valve can stick open or closed and cause concerns going into forward or reverse,working from where the harness goes through the main case and not counting the solenoid on the top of the valve body,it will be the 3rd from the end,next to a solenoid that looks exactly the same.You can removed the solenoid and make sure the valve moves freely."DONT REMOVE the bracket that holds the 2 solenoids closet to the harness pass through, they are very difficult to get back in place properly. If you had no clutch material in the pan,I agree your clutch packs should be fine. Diagnosing your concern would be much faster if you can find someone to read your diagnostic codes with Allison software.
This should be enough info to go as far as you can.