General Maintenance & Repairs - speedometer doesn't keep up with car

So I've been having an issue for the last few months where under rapid acceleration or uphill accel (more load) the speedometer wont keep up with the car.

If i do a WOT run, I'll stop near end of 3rd or mid 4th and the speedo will be showing around 35mph or so pending when i actually rolled into it, and then when I press the brakes it will rocket up to a more accurate speed.

Under moderate accel it will lag a bit until I let off the gas a bit and then it will catch up.

I put in a new VSS sensor and that didn't really help anything at all.

Started when I put in a new Built T56. Any ideas?

instrament cluster, or maybe your wheel speed sensor.

anyway to actually check the wheelspeed sensors short of throwing new ones in there?

Also, my gas gauge is messed up a bit also sometimes it will read nothing when the tank is full and then move up as you drive the car. I assumed that was just the fuel sending unit but now it's just starting to sound like overall something wrong with the cluster