I hope someone can help me with this one.

while highway driving, once i hit 65 mph the truck seems to have a hop in it, it's not a vibration, the back feels like it's bouncing

i put new shocks on, even upgraded from stock

now i had the tires re-ballanced and that helped but the hwy speeds here in CO are 75mph(posted) and when i get going at those speeds it's REALLY bad, but it smooths off if i hit 85mph

the existing tire are goodyear rt/s with a lot of good tread left , and i don't need the expense of new tires if thats not the problem, is there any thing else i should be checking?

the ride smooths out when i hit some dips in the road the starts hopping again and it's worse in the morning when it's colder

 

COuld be the driveshaft or a defect in a tire.

 

you should have them road force balanced.

 

my truck does that when i go between 39-41mph.

it did it when it was stock, with stock tires and shocks, and does it with these tire, and still does if after i put the lift on with new shocks.

it feels like someone is jumping on the rear bumper.

 

the driveshaft could be out of balance, i had to get my 08 rebalanced with only 1000 miles. just an idea to try. either that or there is a belt in one of the tires that is overlapped. it will balance out perfectly fine but on the road it rides like crap. any decent tire shop should be able to tell when they have it on the balancer.

 

the drive shaft has new universals and the rear was replaced about 2 yrs ago, i checked fliuds and they seem to be good

looking back this may have started as a minor problem after i took off the ladder rack

yesterday i was driving a section of road at 75 mph and it road fine but when the road went from asphalt to concreat it started hopping

non of the other cars / trucks i drive have this problem

so i guese i'm changing the tires and see were that gets me

what is force balancing?

 

It's a balancing machine made by Hunter that applies force to the tire while it is being spin balanced. Not all shops have this machine. I believe it is the model 9700.