just got the new speedo put on my 54 chevy 3100 pickup as the other one wasn't working. it all turns and the like but the speedo stops working at about 33 mph. till it gets there it jumps a bit then just sits there at 33mph. someone had put on 215/75/15 6 lug chrome wheels and tires. not sure if that is doing it. i also got the other wheels and tires that were on it prior to that that are 205/75/15's. I would really like the speedo to work. i also have a new speedo cable but havn't put it on yet.

do i need to replace the gear in the tranny or an aftermarket adapter on the side of the tranny that I've been reading about??? thanks mark