I just put in a re-manufactured tranmission into my 99 4x4. Everything was perfect for about 4 days. Now after getting the thing warmed up(10 miles highway or so) it wants to shift very hard to 2nd and a little less hard into 3rd. It fired a P1870 code. Is there something simple that could be causing this? This is a new trans and this definitely shouldn't be happening.

 

GM service bulletin about code p1870

 

Point is.....this thing is new and those components shouldn't be failing after a few days and 150 miles(give or take a few). I'm really thinking(and hoping) that its not the transmission itself.