check engine light on, engine hesitates

well i hope that somebody can help me with this one, i've got a 1995 pontiac bonneville ssei and everithing was working fine up until 3 months ago then i started getting check engine light on and the traction control light on to and then the engone started missing i took the car to the mechanic and he told me that it had po321, po341, po361 codes and thathe would need to replace cranckshaft sensor and cam sensor so he did and nothing the car kept doing just the same so then he decided that the coils and the module was bad and he replaced those and nothing keeps doing the same thing so to make a long story short every single engine sensor has been replaced the ecu checked and the car keeps doing the same thing engine rough sometimes misses check engine light on traction control light on a and i almost forgert the transmision shifts just fine the first time that you starts the car all the way up to lock up but then 10 or 15 seconds later drops the lock up first and then the overdrive and thats it drives in third all the time until you closes and opens the key and it would do the same thing again the mechanic said that he wouldnt be able to fix it and i have spent a ton of money so i need help please ohh and the codes still are po321,po341, po361, po171, po740 and thanks

It sounds like you have a bad ECM. Even though it checks out alright it is possible for it to have a problem that is not showing up on the test. If you have changed every sensor ignition module and coils the only thing left to change is the plugs and wires although you are not showing a misfire code.

I would go to a wrecking yard and get another ecm for your model vehicle. Put it in the car, clear the codes and see what happens. There are too many codes showing up that are related to the sensors that you have already replaced. One other thing if you didn't change the MAF sensor I suggest that you clean it with some throttle body cleaner since that should clear the P0171 code. I hope this helps.