I have a shower stall, sorry I don't know what else to call it. It's not a tub, just a shower with the sliding glass doors. Anyhow, it has 2 separate knobs for hot and cold water. The hot knob is very hard to turn on and off. There is no leakage. It takes both hands to turn it on and to turn it off. I originally (in all my noviceness) thought that the screw that holds it on was screwed too tightly, but that was not the case. I took the knob off and tried to turn the stem with a pair of pliers to see if it was maybe the knob or the stem. The stem was still hard to turn. I'm not sure what to do at this point. Any advice would be appreciated. Thanks in advance.

This may be over your skill set but I'd disassemble that stem. Once you take one apart might as well replace the washer and seat. When you tighten the packing nut just stop when you feel the knob starting to tighten up but not leaking.