Why when my car gets hot does my transmission stop working and my car feels like its in neutral and won't switch gears. It will cool down and start working for a little bit until it gets hot again.

first service the system...if no better..time to rebuild it..

Transmission service s just that: a "service" not a repair or an overhaul in a can. IF the unit had been serviced at somewhat regular intervals, then most of the overhauls I did would not have been so numerous. On the off chance something just broke or individually failed in that unit .... well, it's all academic if the trouble is inside the case, isn't it? FWIW: external linkage problems are extremely few on Hondas .... but get a real transmission shop to look it over .... where you've gone for all your transmission services in the past. Errrr, cancel that last part. Seriously, transmission services are for maintenance. ... not repairs when something's gone bad.

Had the same problems on a 2000 civic no trouble codes given. When cold it would shift from 1st to 2nd and 2nd to 3rd and 3rd to 4th no issues. When worm it would start to delay the shift until it would neutralize. The car would not move forward I would park the car for 30 min to cool down and it would work perfect for the next 20 to 30 min. The problem was the input speed sensor was bad had weak signal..