94 Toyota Pickup Overheating

Hi everyone, i have a 94 toyota pickup v6(3vze) 4x4 manual with 210,000 miles. It's been giving me problem after the overheating and no sigh of leak head. I recently change 2X T-stat, new water pump, timing, radiator, and every other small part i thought it could be. This is my second time rebuilt engine and my first time having this serious overheating. Cant find any leak but engine idle went unconstant and roughing. Have a hissing sound on maniford and hot air in muffler. I even take out the t-stat due to high temp gauge but still blow hot air and in 3/4. Any ideas?