Toyota Repair: Check Engine Light Code #25 1994 Toyota, coolant temperature sensor, air fuel mixture

Question
I have a 1994 Toyota pickup that I just put a 88,000 mile 22-RE engine in. The truck has 300,000 miles on it and is a 5 speed transmission and is 4 wheel drive. My check engine light has come on and I done a test on it and it comes up code #25 Air/Fuel mixture lean. I replaced the O2 sensor 3 times and this last time with a Toyota specific O2 sensor but it still comes on. The truck runs and idles fine cold or hot but is using gas bad and leaves a bad gas smell like it's flooding bad.I've changed the cat converter and changed the coolant temperature sensor and check for air leaks in the hoses and lines and I've also cleaned the MAF sensor or I hope I cleaned it right. If I unplug the battery and reset the computer the light comes back on after 20 miles or so of driving. I am stuck and don't know what else to do. Any ideas would be greatly appreciated. Thx  

Answer
By now you know that replacing O2 sensors is not going to fix the problem, the O2 sensor is only reacting to what the problem is,if the engine is running and idling with no misfires it means that the lean run condition is due to an external fuel leak, have you checked to see if there is a visible fuel leak, the engine can't be flooding or there would be a bad driveability problem but you say the engine runs fine, this would rule out a rich run condition which would also mean there is black smoke from the exhaust, this is not the case.