Man...this sounds like a nightmare.
Reminds me of my 93 GSX Eclipse. I took it to a shop because it would start to bog down and barely accelerate. The shop charged me $100 and said everything seems fine, LOL.
It kept doing it so I sold it.
Cut to years later I own a Dodge Stealth. Whoa...it has the same problem. Ends up...the CPU's die and need replacing. The whole car had MAJOR issues simply because of the CPU...which is sooo wierd.
It was blowing white smoke out of the tail pipe and everyone said...uhh oh...coolant is leaking into your engine...you're screwed. But.... As soon as I fixed the CPU...the bad, foul, white smelling smoke...gone.
Cars can make you insane when they have "gremlins".....