reverse lights wont stay on unless i wiggle the shifter

[1972BlueC20]

My reverse lights work, but they won't stay on when I put my truck into reverse. I have to hold the shifter a little to the left of R to have the reverse lights stay on. When I let off on the shifter and let it fall where it does naturally...the lights go off.....the shift indicator line up pretty much perfectly with all the gear indicator marks....is there an adjustment I can do to make the reverse lights stay on at all times when the truck is in reverse gear?

I have a TH350 automatic BTW


Thanks,