Q&A

 Master

I assume your're talking about an automatic transmission, not a manual. It's good to include in your question the engine size and transmission type.
If you are suddenly experiencing hard shifts, the transmission may be in a 'failsafe' or 'limp-in' mode because something's amiss with the transmission system. I would think that the 'O/D' light or some trans related light would have come on to indicate the fault condition.
Check your transmisson fluid with the engine running and the park brake on, on level ground. Vehicle should be fully warmed up. The fluid level should be in the crosshatch area, free of foam, pink and clear with no burnt odor. If the fluid's brown and clear, but not burnt, that's OK too. If the trans is overfilled, it will cause foaming and shift problems, but I'd think it'd be a soft shift, not a hard shift. if you have to add fluid, use only Dexron III(R) fluid.
If a malfuction indicator light comes on, then the controller has detected a fault, and has stored data and trouble codes which can be accessed using a scanner.
Here's a directory link for you:
http://repairpal.com/directory?address=64030&car_brand_na...

hard shifting is common in old cars and vans.DIRTY TRANSMISSION FLUID ADDS TO THE PROBLEM.dont change the fluid as this will change internal pressures and possible make it WORSE.AD LUCAS TRANSMISSION ANTI SLIP ADDITIVE FOUND AT ANY AUTO PARTS STORE.if theres no room use a siphon pump at filler tube drain a quart out.THIS SHOULD HELP.