TOP END PROB..............

Explain the popping sound in a little more detail. How long does it last? Is it more of a ping (knock, detonation) or like a backfire type of pop? Also, is it hesitating while making the popping sound?

That shake at 70 mph is the inbalance in the stock driveshaft that is made more noticeable from the gears (or so what i read). Get a aluminum drive shaft and you should be good to go. That was problem and a new driveshaft solved it.

As for the gassy smell, i would guess that would be its rich so maybe the o2 sensors? Im not positive so hopefully more experienced guys will chime in.