Suburban :: 1997 - Shakes Vigorously At 65 - 75?

First i know this subject has been covered, but i am at a loss. I have a 1997 burb 2wd that started the shake right after i bought it. it shake from around 65 to just under 75. Here is the list of items I have done by reading the forums. I am on 2nd set of tires both different brands. Last set has been road force balanced new inner and outer tie rods new shocks new rear trans mount new front and rear u joints had drive shaft rebalanced new front wheel bearings this is also the other stuff that has been done in last 6 months new a/c compressor and lines new alternator new radiator new plugs , cap, rotor, wires. It is hard for me to tell where the shake is coming from as sometimes it fells like the whole truck and other times just the front end. at this speed i also have put the truck in neutral and let it idle down and still nothing.