1998 Honda Accord transmission shifts too early

My transmission shifts into at 10mph, 20mph, 30mph and so on. I checked the voltage on both the tps, and map sensor. Both checked out fine. I have no check engine light. I checked with a computer anyway and nothing came up. I was wondering if it could be something a little as a cable needing adjustment, the vss sensor, or maybe a possible transmission problem. Have any ideas?

by the way, I replaced the spark plugs, wires, rotor, distributor, air filter, transmission fluid (honda atf), and I change my oil every 3000

i would appreciate any help. Thanks