I've looked for an answer to this before but have been unable to find one, so I figured I'd make a new post. I have an 01 4.6 xl f150 with cranked t bars+ blocks on 315/75s. Probably about 3" of lift.
When driving in the 40-45 mph range, the truck bounces. This can range from an "annoying" level to becoming enough to evoke road rage. It dissipates under acceleration and once out of the 40-45 speed range. Also, when braking, especially when in the 40/45 speed range, the truck hops.
Other than this issue my truck is great. However, I just turned 18 and am not in a position financially to start flinging money at my truck, seeing if doing x will fix it. I considered getting a real suspension lift kit, but I don't want to if the shocks aren't the issue. Anyway, If anyones dealt with this before, or has any good guesses on what it is, I would really appreciate the help.
Thanks

 

My first guess is your shocks. When the truck is parked, push down on each of the corners. The truck should bounce maybe once or twice, and settle quickly. If it just keeps bouncing, you have bad shocks. Shocks aren't too expensive. Usually 30 dollars each. You may also have turned up the T-bars too high. This could be hyper extending the shocks. Look into longer or higher quality shocks.

Heres a wikipedia post about torsion bars. There is a section in there about turning up your torsion bars too high.

https://en.wikipedia.org/wiki/Torsion_bar_suspension