My 2003 Kia Sorento shakes in the rear after hitting a bump however when you come to a comple stop it stops shaking?

Thats called a shimmy. And you have shocks instead of struts.
Chances are you have a ball joint or tie rod end about to fail. Something is very loose in the front steering or suspension. I'd put money on it being a ball joint.

NO PUN INTENDED. If u are asking about "if its a shock absorber" I professionally advise u not to tackle the repair. It may not even be a shock we're referring to.

it may sound stupid but if the air filter is dirty it wont get enough air so it will shake badly telling you for experience

I can't see the T/Belt giveing that problem however if the T/Belt is due it should be done ASAP because if the belt breaks it can cause pistons to hit valves (Very expensive to fix) but could be the catalytic converter or a number of other things. My thought would be to undo the o2 sensor in the exhaust & run car this will allow exhaust to escape without going through the catalyst. If car stops slowing to a stop you know that the catalyst is blocked. Or remove the catalitic converter & look through it it should look like honey comb you can see through. P.S your car posibly won't go without the o2 sensor in.

have the struts checked

Sounds like a bad wheel bearing to me. Jack up each corner of the car one at a time and grab the tire. Shake like crazy on it - if it moves, you've found a bad bearing. It should be solidly on the hub with no play whatsoever.

Check your wheelbearings for play and your tierod ends for play,I'm sure one of these two are at fault.

Have a cylinder leakdown test done...likely they missed another bent valve. I'm betting it's an exahust, because it would be less drivable if it was an intake, but regardless, I'll bet that is your problem.

90,000 MILES

Check your stabilzer links