Tranny problems!!

[NewGuy]

About three weeks ago i purchased a 98 s-10 4.3 4x4. When i test drove it after the first stop i came to it felt like it popped out of gear (automatic) i had to take out and put it back into drive to go again. i told the guy i bought it from and he said if a had any future problems he would have it rebuilt for me. Anyway i had it rebuilt last week and just got it back one week ago today. I had no problems until yesterday after driving it for awhile i noticed my service engine light was on. i took the truck to a garage to have the codes pulled. they found 1870, from what i was told this is a tranny slip code. my truck is banging in gears when it shifts. i called the place where the tranny was rebuilt and told them my situation. He replied that this sometimes happens after a rebuild and that qonce the codes are cleared there should'nt be a problem. He wants to reset the codes for me tommorrow. is this true?? has anyone experienced this problem?? there are 86000 k on the truck

             Thanks Brian

 ???

[CTRDRV55]

My truck never popped out of gear but it started slipping and the SES light came on.I would be driving and it didnt want to go out of second,then when I got off it the rpm just dropped.When I got back on it the rpms went up and then it went  BAM into 3rd.I took it to my dealer right away and they said they would have to look into it.I ended up getting a new torque converter and havent had a problem since.