99 discovery i had a misfire/vibration problem, i got the tranny codes and the lean codes indicating MAF was bad, replaced that and the vibration under acceleration deffenently got better but is still very evident. i checked the wires and changed the plugs. it also has a new CKP sensor. i dont see any evidence of any kind of vacuum leak either..

 

How many miles on your truck? Have you replace the factory ires, have you rebuilt the front drive shaft, specifically the u-joints in the double cardon which are know to fail.
Mike

 

there are 100,684 on it. it s got new tires, and driveshaft is original, there is a squeaking sound coming from upfront under acceleration.. how can i check the ujoints

 

If the front drive shfat u-joints don't have grease fitting in the constant velocity joint where it hooks to the t/case, remove them ASAP and have all e of them replaced.
At your mileage, if you are wanting to improve your mileage and performance, you will need to due a few things, replace the plug wires, using a set of Magnacor 8mm wires, flush the engine, do an induction cleaning and start planning on replacing your o2 sensors that are warn out at your mileage.
Mike