My fuel pump failed this spring.
It started as a curious intermittent hesitation, then 2 weeks later dramatically escalated to a pull over to the side, wait, restart, drive a while, pull over to the side again situation. Giving the pump a solid whack made it run an hour straight so that I could get it home. [As an aside- do not buy an Autozone pump. Works fine, but fits poorly, and is very loud. Saved $25 over Bosch-by-mail, and got it on a Sunday, but still not worth it.]
That would not explain the onset after cleaning the engine, since the fuel pump is in the back.
You could try replacing the fuel pump relay just to see if it helps, since this is easy. These reportedly fail frequently, and I have been told they can be intermittent, though the one I know of was a total failure.
Replacing the pump is a pain, mostly because you need to drain the tank. Same deal with the filter [this is a very poor design, I might add...]
Your filter could be clogged, ot the pressure compensator device (next to the pump and filter) could be failing.
None of these problems are related to your cleaning event, so if that was definitely the event that started this problem, I would look elsewhere. Still smells electrical, but I have no new ideas to offer on that end...
I do not think that the pressure release when you remove the gas cap is related, however. Someone else may correct me, but I believe that effect has more to do with temperature differentials expanding or contracting the air in the tank.
1986 300E 5-Speed 240k mi.