I have a 1976 F150 4x4 with a 360 and C6. The truck is mainly used for hauling trash, etc. and often sits for a month or so without regular use. The transmission has always worked OK since I bought the truck two years ago, but when I went to drive is a few weeks ago it would no longer shift into 3rd gear. It had sat idle for about 6 weeks before this. The last time I drove it it didn't have any problems and I've never known it to slip or anything. I checked the fluid level and it seems fine. Not sure about the color since i'm not familiar with automatics, but it doesn't look real dark or smell burnt. I also checked the vacumn hose from the carb and it looks OK, although I didn't try clipping off a few inches to get a better seal. I asked a couple of shops and both said they thought I needed a rebuild and quoted ~$1200. Neither of them actually looked at the truck. I can't see spending a ton of money on this old work truck so I started looking for used C6 but no one in my area has one. The yards all said I was looking at around $250 for an exchange. Is there anything else I can check/try before I replace this thing? I can't believe the tranny just self destructed while sitting for a month or so. Any advice is welcomed! Thanks!