Differential problem ?
 

I have a 2001 with 24 vales got it about 2 years never change any trans or gears fluids since i got it just done what i got to , to have it going ... Using a super chip tuner since then and some basic mod ... Problem just stared about 2 months , every time i made a 90* turn i felt my truck is lag of power , some time idl trop a bit and power is keep on laging even i give it a litle gas up , but then every thing is going back to normal when turn is complete and the truck is just speed up like a rocket ... Any ideas is help ..... Thanks