t-400 trouble

[chevy406]

hey everyone iv'e been lookin over the site for a few months and finally have a question to ask this is prob a stupid question but im working on my dads 79 k20 camper special and cannot figure out what is wrong with it. while driving it last night i noticed that it takes it awhile to go into second gear and it wont even go into third i checked the tranny fluid and its fine my dad says its the tranny module so im trying to take off the vacum module on the side of the tranny and i try spinning it off and it wont come off. what am i doing wrong? any help is appreciated. thanks and the forum rocks!