Stupid question but making sure its just engine knock you are hearing and no associated vibrations.

Bad U-joints will show themselves going up-hill/accelerating. But you wouldprobably feel a vibe in the seat of your pants along with the knocking noise.

Just thinking out of the box!!!!!!

 

I can almost gurantee it's your intake plenum gasket. If you add Sunoco 93 or 94 octane it will probably go away since that will help reducespark knock. But as soon as you use 87 it will come back, do yourselfa favor and go spend $35 on the gasket kit.