rattle noise driveing me nuts!! help?

i have a ratttle (tinny)noise coming from mid vehicle. tried replaceing complete exhaust(needed it anyway)tighten fuel tank skid plate, and bang on every thing with a rubber mallet. nothing rattles parked or running in gear while in the air. it only does it when driveing on road under load. loudest in 2nd,3rd,4th 5th ..gear. around 1500 rpm. sounds like it may be driveshaft u-joints. i greased them all but noise stays the same. it also have a vibration when first letting clutch out in every gear till maybe 2500 rpm. i think it has u-joint issue but not sure. are u-joints a problem on these trucks??? its got a 31 in. tires ,2.0 suspension lift and its a 96 extracab 4x4 5spd 2.7l...w/185k