i got a problem, my speedometer tweaks out. lets say id be driving 45mph on neutral and would put the car in gear, the speed reading would drop 10-15mph, same with downshifting, my speed reading would decrease if i would downshift. what could be wrong? where do i need to look? where is the speed sensor located?
thanks

 

out of sheer curiosity, are you running the stock 4.10 final drive?

 

Out of sheer curiosity, which mods are you 'forgetting' to mention here?

 

Do you have a yellow box or yellow jacket for speed correction? Do you have a piggy back controller spliced into your wiring harness? Do you have an EMS?

Usually, the wire that goes to the ECU gets pulled or pinched or messed up in someway to cause the problem you describe.