Im having Speedometer issues!! HELP!!

[1970K10NamedCrunch]

Hello. So, I am having some issues with my speedometer. When I'm driving, it works fine till i get to 35mph. And it stops. It stays at 35 mph.. Then I slow down, and it comes down to about 23mph, and it sticks there. I have to tap the speedometer to get the needle to drop. The whole gauge cluster is original, other than Water Temp.. And the speedo has a new cable, just oiled a few weeks ago, and that didnt help either.. So what could possibly be the issue? I need help. PLEASE!! I pulled the instrument panel out of the dash, and the oil pressure gauge wouldnt come out of the back of the o.p. gauge.. But i also didnt drop the steering column either, so maybe that will fix the Oil Pressure gauge. Please help!! Any advice or suggestions would be much appreciated. Thanks.