Chevrolet Repair: 1999 silverado ls 2500 hd, drive shaft, plow truck

Question
i have a 1999 silverado 2500 hd with the automatic transmission and push button four wheel drive i recently purchased. the previous owner had a snow plow setup on it which he removed before i bought it. my question is i have a bad vibration at high speeds starting at about 45 and getting worse at higher speeds. the previous owner had a new front drive shaft put on, the  yolk replaced on the front differential,all new u joints both axles, both axles balanced and the transfer case gone through all by the local cheverolet dealership. I have replaced the tires and still a vibration. i unhooked the front drive and it quits.  i tried pushing the four high and four low buttons and it sounds like it is engaging and disengaging. any help would be appreciated .

   thanks for taking the time  Jamie

Answer
the vehicle has been used to driving witha plow on the front and now is dont have one. sounds like the front end took the brunt of all the plowin. as for what you can do, not much short of replaceing the front end works.  it was used as a plow truck and that is what its used too.  keep it out of that front drive as mch as possible. but maybe you can get a second opion if ya dont like mine.. sorry.


keep me psoted