XTC's came with the same shocks that SXR's did, Vipers too. It's all in the valving, and you already have 'long travel', not like the SX's.
If there's alot of miles, you might be able to get by cheaply, like MrSled said, by just having them rebuilt. If you don't have alot of miles, and the shocks are ok, then I'd recommend making sure the suspension is set up for your riding style and weight. You're looking for a 50/50 rod gap with the FRA adjuster in the middle position, adjust your preload on your rear spring until you get there.
Check the tech page for suspension set ups. Also, give some more info, and we can help ya better. Good luck!