I recently rebuilt my 741 Power Loc Clutch typ differential and as instructed by Doctor Diff I applied pleanty of LS additive to the clutches and plates. Everything went together smoothly and the car is back on it's wheels.On the street, under low acceleration or even idling around the rear diff is super tight (locked). I have not had a chance to put many miles on the car yet but is this normal and should I expect the dif to loosen up some or do I need to be concerned about how tight the diff is?

Thank you in advance.

Find an empty hard surface parking lot and do 10 slow tight figure 8s one direction, then do another slow tight figure 8s the other direction. Expect to hear a lot of strange noises, its a sign the process is working.

I suspect the friction plates are dry between them. The figure 8s force the plates to separate so the fluid can get between the clutch discs.

If that doesn't do the job, its probably time for a rebuild.

Did you buy a clutch pack for an OEM power-lock or an aftermarket power-lock?

If you are installing an clutch pack intended for an aftermarket power-lock, you must re-use your original thin plates on the end of the pack.

I purchahed the 8.75 "internals kit" and bolt kit through Doctor Diff (thank you!!!) and the clutch pack was a NOS Spicer pack a friend had on the shelf from years ago. The steels were identical from what I could tell but I did not put a caliper on them.
I can try the suggested above... with that said, nothing was dry during the install, everything inside the Power-Loc was well lubricated. I made certain the Ford LS addative was covering everything inside.

If it was in a Spicer box, you have a Dana 44 power-lock clutch pack. You must re-use the original 8.75" thin plates on the end of the pack.

Well damn it.... thank you for the info

OUCH!!!! We appreciate your knowledge & inputs
Maybe a 1000 figure 8's each direction ?