2011 Ranger bucking and missing going DOWN hill

[greglewis1]

I just had my 2011 Ford Ranger 2.3 4 cyl engine worked on. Had two dead cyl and found 2 burnt valves. Had head reworked. Now I have a perplexing problem. Uphill and on level the engine runs like brand new (179,000 miles now) but when I go downhill the truck bucks and misses like crazy. It stops if I accelerate but if you try and keep a steady speed (cruise control and manual) it is horrible. Doesn't even have to be a major downgrade, even does it on a slight downhill slope. Replaced MAF, plugs, wires, coil, etc.

Does anyone have any suggestions????

Thank you in advance.