Hello everyone, new to the group and need help. I'm fairly good around cars but I need expert advice before proceeding. My GF has a 1996 Blazer with 125xxx miles. 4x4 2 door. V-6. She says the transmission was replaced at around 6000 miles but I personally don't know. Anyway, yesterday I was taking it to the carwash and it wouldn't shift from 1st to 2nd by itself. Threw check engine light. I stopped the truck and put it in 1st and shifted the transmission myself. Shifted 1st to second like it should but when shifted to drive it just reved up. I took it back to her house and checked the trans. fluid level. Showed 1 qt low. BTW the blazer sits inside and nothing under the truck leak wise. No drips either. Anyway, I added a qt of trans. fluid and it shifted through all the gears as it should. I drove it about 6 or 8 miles and returned with no problems. This morning, same issue, wouldn't shift by itself. Trans fluid it showing full and still no leaks. Low gear and reverse seem fine. As you probably know by reading, the truck only gets driven a few times a year but it is near showroom condition. Ideas? Suggestions?