new rear now MPH is wrong

[fordkid68]

hello every one.


well I just got done changing the rear ends in my 66. and now my gauge is saying I am going slower then I really am. could this be cuz maybe I have diferent gears in the new rear end. I thought they were 3.20(the same that is in my old rear end) but maybe I am wrong maybe there 3.25 or something ellse. but maybe I am way off track. here is whats going on. it will say I will be going just under 20 but the engine sounds like it is winding up higher then that. so I shift to second(it is A 3 speed) normally I thought you could go 25 or 30 before your engine really starts to wind up as high as it was. and once I get to about 30 it will just plain stop going up. I even took it on the freeway and was pacing with the other cars and it said I was going 33 to 35. it wasn't staying in the same spot. so what do you guys think is wrong.

other then that I had no problems changing the rear end. witch is why I am conserned about this problem cuz normally no matter what size job you have you always will have problems. so is this going to be hard to fix or what.

well tell me what you guys think is wrong.


thanks
ford kid