How to check a cylinder?

I have recently undergone the task of learning my own motor instead of relying on the local repair shop to keep messing it up. I had posted earlier about how out of whack all my adjustments were. Once I got them fixed it ran great. Last tourney however, after I would run for 5 or so minutes I would lose about 3-400 rpm. It would occationally pick up but not real well. The consensus was that I should check my fuel pumps first. I replaced them and took apart the old ones and did not see much wrong. The guys at hydrotech said to make sure I do a compression check because my motor had been so out of adjustment and timing that I could score a cylinder. Well.... I checked twice and I am 120 - 140 - 140 - 145 - 145 - 140. Looks like a problem with my #1 cylinder.

Any suggestions on what to look at? Shop manual shows how to take it apart but what do I look for and how do I fix it? '97 200 ProV.