Ok, so this problem recently started within the last month.

TH-350 all stock, no shift kit. Bolted to a 327(if that matters).
B&M megashifter (3speed) with bracket and leveler kit and B&M 5 foot universal cable.

When vehicle is not running, I can cycle the shifter through all the gears and it is changing gears on the transmission. When running but cold, I cant get it to engage any gear, the rpm's lower slightly (maybe 200 or so) when I select a gear. But still not engaging in the transmission.

However, once it has warmed up quite a bit, it will shift into all gears smoothly and will rachet just fine.

I've tried re-adjusting my cable/bracket but to no avail.
Fluid level is fine.

What could it be, low pressure?

Any help would be appreciated.

 

I would suggest that you check the fluid level