2008 wont go over 20 mph
 

i have a 2008 extended cap 4x4, the rear end locked up and blew apart so i got one from the bone yard and put it in now the truck wont go over 20 mph!!! can anyone help??

did you match the gearing to the front axle?

Did you scan for trouble codes?

Likely on the money, MMJ. The ECM can likely detect a difference in the gear ratio of say a 3.42 and a 4.10 axle, so it compensates by slowing the motor down. That's gonna tear something up if the axle ratios don't match for sure.

gearing is correct and no codes.... its my sons truck and now he tells me it started just b4 the rear end went out

Gonna have to give us lots more information if you expect us to be able to Dx the issue. What have you done so far?

so far only swapped out the rear end

Can you be more specific? Like is it just not shifting out of 1st, or the engine is hitting an RPM limit. You need to walk us through exactly what happens when you drive the thing.

Maybe you just knocked the speed sensor loose when you changed the rear axle.

When your driving normal in drive the truck acts likes it has a engine brake at 20mph..I tried to manually shift it and 1st gear works fine but then ur at 5k and try to shift time 2ed it just starts to rev up and slows down like its braking hard.

are the brakes stuck?