I have a 98 1500 Nomad and have lost drive power twice after a long ride. The gears seem to shift well in the beginning and continue for a couple hours. I will stop and take a break for 30 Min - 1 hr and then the transmission will not shift and the clutch seems to be partially engaged or not engaged at all. Any idea what the problem is? Richard J.

Contaminated fluid in the hydraulic clutch actuation system. Instead of a cable, your bike has a hydraulically actuated clutch. This system is great because it offers low maintenance and a relatively light clutch lever pull.
You will need to flush the system, refill with the appropriate fluid (check the owner's manual, but it is probably DOT4 brake fluid), inspect for leaks, and bleed.