If you can shift through the gear while sittling still and the engine running (clutch pushed in obviously), then I wouls guess that it is probably not a clutch problem. I have heard of new fluid in a tranny making it shift easier (especially when switching to synthetic). But i don't know if it would help in a situation as extreme as this.
Project '94 YJ 2.5L Four banger w/AX-5 (for now), Ford 8.8 locked out back, D30 up front both w/ 4.88's, SOA on stock springs, 1" Lift shackles, SYE w/ CV driveshaft, No new tires yet still deciding on size (Prolly 35's)
DD '03 F-250 7.3l PSD w/ ZF-6 6 Speed. Ford Makes It, International Shakes It. Real Trucks Don't Have Sparkplugs