2002 Accord 2.3l SE sedan auto transmission, Japan built, with 99500 miles, stock everything. Almost always the transmission revs from 2.5-3K rpm in order to shift from 1st to 2nd, kinda like it's slipping. But the car speeds up really slow until 2nd gear. Then when it finally shifts into 2nd gear it's fine.

When I bought the car it shifted excellent, like a manual, like the transmission was shifting by looking only at the rpms. I am using 87 octane now but when tested and bought at dealership I am pretty sure car had 91 octane in it. It can't be that the transmission broke after 5 months of driving if it drove excellent at the dealer, even though the fluid has not been changed before me at 99000 miles.

So far I have replaced all of the solenoids and did a drain and fill 2 times. Will do a 3rd drain and fill in a month. Have not replaced the countershaft speed, mainshaft speed, TPS, MAP, or IAC sensors. Both oxygen sensors have been replaced. It's just reving too high when shifting from 1st to 2nd with very little torque it seems. Throttlebody is clean. It shifts much better when the engine is warm and when I step harder on the gas. And no engine codes were thrown for anything since I bought the car 6 months ago.

Anyone have the slightest idea? Possible 1st/2nd clutch worn out? sensors?

 

Check for codes, not all codes illuminate the D4 or CEL lamps.
If the shaft speed sensors are dirty or fouled, and with the fluid never changed this most likely is the case, they will not read the correct speeds of the shafts and will shift erratically.
Just pull the two sensors and wipe off any magnetic slurrry on them, it will be the same as the drain plug if they are covered.