So merc says that ujoints and splines will show premature wear if I don't use their special grease. Is There anything better?

Boy, I hope not,.... I've been usin' plain ole chassis grease for the last 30 years,.....

Actually the u-joint and spline grease are two separate greases. Both are fairly cheap and you don't go thru a bunch so I just buy the Merc stuff. U-joints and gimbal bearings with one grease and the splines with the other. Something like the red Lucas would probably work just fine and you could also use it for the trailer wheel bearings.

I use regular grease for u-joints, just don't use anything with Teflon in it. The stuff is so slick the needle bearings may slide instead of roll