Clunk, clunk, clunk, goes my 1999 Ford Ranger

 
I have a 1999 Ford Ranger, V-6, 2WD, 71,000 miles. It has a clunking noise that sounds like it is coming from the front or near the front of the truck. You can only hear the noise in hot weather, and after the truck is run for a few miles. The longer you drive, the louder it gets. I have replaced the upper and lower front ball joints, upper and lower control arm bushings in the front suspension, Sway bar bushings and links, outer tie rod ends, shocks, and coils spring insulators, also all in the front of the truck.
All the body mounts are tight and look to be in good condition.
The bolts on the rack and pinion steering are tight.
I removed the drive shaft and cleaned and greased the splines. I also replaced the back shocks.
I tried riding the brakes, but the noise does not stop.
I have had this noise for over a year, and no one can find the source, not even my Ford Truck dealer.
I have been over the entire truck several times and everything looks fine, and the Ford people agree.
As I stated this is only in hot weather. I live in Florida, so we have a lot of hot days. In the mornings if it is 60 degrees or less, I can drive for half an hour and not hear a bit of noise.
The noise sounds like when a stabizer bar is loose, or exhaust is clanging against the frame. But both of these items have been checked several times.By the way, this noise happens when going over an uneven road. It can be heard more on a wavy road than it can on a bumpy road.
Thanks, BillJ