How much weight are you carrying? I'm pretty sure you're not close the cargo capacity of the truck. My guess is you have less than 200 lbs in the bed.
A wavy, bouncy feeling is likely from worn out shocks. How many miles on them shocks? General rule of thumb is 50,000 miles to replace.
The set on my truck were installed at 75,000 miles. I'm knocking on the door of 125,000 miles, already beginning to feel some extra bounce. So, setting up the budget for a set of shocks for the Tacoma. Probably a task this summer.
Just replaced the set on our '02 Trailblazer. Embarrassed to say, those were OEM shocks with 130,000 miles...........they were long past due. Absolutely, zero rebound when compressed by hand and little resistance when compressing by hand. But they didn't leak.......