First thing to check is vacuum. A leak anywhere in the engine compartment or HVAC system will cause harsh shifting. Change the fluid and filter. Next, bowden cable adjustment. An easy check is to temporarily plug a vacuum gauge into the modulator line and see what the readings are when you are driving. If you have a funky 2-3 shift, the K1 accumulator spring would be worth checking/replacing. That's the easy stuff, reassess when that's done.