Q: Car will not properly shift into gear, revs up, then shifts

Have a 1998 Honda Accord. Once I bought the car and I drove it , it rode very fine.. until I thought that I had a bad transmission after I discovered it had trouble dropping into gear and it will not rev above 4000 rpm, it starts to shake. I do know i need motor mounts , like 2 of them and that my oil level was pretty low at one point, i changed the oil but i still have the same problem. when i start the car up in the morning and drive it rides fine and drops into gear , all for about 20 minutes with no problem but still wont go above 4000rpm. I drained the transmission fluid and took it to a transmission shop, they told me i need a transmission but i don't think need one because they were supposed to tell me why my car was acting like that. i got to mcdonalds and just decided to take a peak under the hood and discovered myself that the entire intake hose was cracked and i replaced it and spray carb cleaner inside the throttle and it rode a little bit better but still has a problem

My car has 280000 miles.
My car has an automatic transmission.