Guess I've been lucky as my pitman arms have always slid right off with just a little bit of pry bar help. Like Robyn said, remove the bolt. I spent a good amount of time trying to remove an arm while the bolt was still in place only to realize that the bolt goes through an indent on the pitman shaft. Once I discovered my stupidity, I pulled the bolt out and the arm practically fell off. Keep trying, you'll get it.
Mark Chapman DP member #653;
1983 K2500 6.2 Suburban, 4" lift, 35" tires, ATS turbo, Banks exhaust/intake, pyrometer, tachometer;
1986 K5 6.2 Blazer, 2" lift, 33" tires, Banks intake, pyrometer, tachometer
1963 wife, one owner, average mileage for the age but in excellent shape, a keeper
1992 daughter, low mileage, pretty, limited edition, but requires some money to maintain
1995 son, sports model, very fast & peppy, time will tell on durability and maintenance costs
"Grease is good"