simba abrams

I have a 04 MDX with 166k that starts up fine. But when i hit a hill it seems to go into neutral. So i put the vehicle into neutral and back into drive and it re-engage and drives fine. It only happens when i first start to drive but after the vehicle is all warmed up it drives fine with no issues. Also hesitates when going into second gear don't know if that's the solenoids or if it just needs a tune-up or just changing the transmission fluid and filterthat is turning brown