Gear ratio and cpu

is it a 4X4? and did you change both axles? if not then you suv is fighting its self to go forward due the difference in gear ratio.

Yes its 4 wheel drive and i did switch both differentials so that they match.. i have asked alot of people and noone seems to know everyone is puzzled.. there is no slippage or anything in trans it just out of no where will go into limp mode

It should still run and drive like normal just with the speedo off by a few mph. I'm thinking you have another problem

ok so heres my next idea, try driving it maybe 1 mile or something listen to the motor and transmission and suspension, if you hear a roaring noise (like a motor in over rev) before stopping check your RPMS on your gauge and if they are above 2000 then its you motor makig the noise HOWEVER if its not lift the vehicle and rotate the wheel by hand and listen for grinding if it grinds replace the wheel bearing on that wheel. or if none of the above check your transmission fluid level, color, thickness, and smell, and don't forget to check the fuses and stuff it could save you some work. also while your at it check oil level and color. if no results just get back to me and i will help you further

All 4 wheels and tires have to be the same size on a 4x4