Clutches set up for racing do engage at a higher RPM. But if you've got a pretty stock XLT, then it should have close to stock clutching. Since you don't know the entire history, you're better off rebuilding or at least cleaning the clutches anyway.
Pull the primary springs and weight, look for sighs of wear on the weight pins and bushings. Compare the springs and weights to what you can find in the parts catalog. Also take a look at the spider buttons too see if they are gummed up, the buttons and towers might need some degreasing.
Take the secondary apart and again compare the helix and spring to what's in the parts catalog. Look closely at the buttons the helix works against as they may need to be replaced.
Once you get everything all cleaned up and put back together you can install the primary back on the sled and run the engine without the belt in place. The primary should slam shut around 1400-2000 RPM, but I don't remember exactly what is was supposed to be. It's been a long while since I've ridden my XLT.