Intermittent start up issues

Transmission total soft and partial hard rebuild three months ago. Front engine collision two months ago. Changed ABS relay and verified radiator and A/C function at that time. Regular oil changes and service with certified Honda mechanic. Premium gas only. Additive/cleaner every third tank of gas (Lucas). Only run to half a tank, then refill. Kept in garage for overnight until two months ago. Three weeks ago horrible rain storm. Next morning started car, backed out of driveway, put in D5 and moved forward by pressing accelerator. It seemed to drop power and rpm's, then sudden surged up to normal. This freaked me out as my first thought was transmission. I pulled over and sat. Put it in park, then tried again. Same thing. I then decide to turn around so pull up a few feet and I can just feel it drive like normal. No lights. Called my mechanic he hooked it up, no codes. He checked a few things (not really sure what), test drove it. Nothing. Four days later after rain, same thing. So I started backing car into driveway and had no problems until yesterday (Monday). I also filled up gas on Sunday. Horrible rain storm again. Monday I start car (which has not problems or hesitation) however it felt it a small tremble so watch rpm's and they are dropping below 500 (500 is normal for my car), so I rev engine. I had no problems. Come back to house, twenty minutes later go to leave and drive away (without backing out) and it starts bounce rpm's and acceleration. I drove fine to stop light, then upon acceleration is drops rpm's the suddenly "kicks in" and I am flying. It drives normal after that. Leave it sitting for eight hours and I have problems again but acts like it wants to stall and then jerks ahead. This time all my lights go on (VSA, caution and check engine). I get home and check gas cap, and it has "popped up" so re-seat it. It rains. I go to leave later (lights are off now) and this time I sit and rev engine. When I release rev with driver door open I hear a loud hiss from I am not sure if hood or back of car. Each time I do this the hiss gets shorter and less noticeable until it is gone. This I drive away and have no issues. I am taking it back to my mechanic, I do not know if he will get any codes except the gas cap code. I cannot find anyone with this problem, similar yes, but it is so specific.