1998 Z71 shifting problems DTC P1870 found

[maybizzle]

a week and a half ago i was driving my truck and it started shifting real hard at 20mph and again around 40mph. 30 min later the check engin light came on. i went to my gm dealer and my buddie got a "crankshaft position sensor" (CPS) code. i replaced the sensor in the parking lot and reset the code. all was fine for a week. i was on a road trip, had been driving for about an hour, and came to a small town and hit a red light. took off normal and BANG hard shift at 20mph. i drove around for about 10 min and it kept doing it. i parked the truck right away and rode the rest of the way with a friend who was following me. several hours later i got the truck and drove home(another hour of highway driving) with no problems at all. havent gotten a check engin light or expericenced it again since. today i went back to my buddie at gm and he ran it for codes and got the P1870 code and printed the diagonistig procedures for that code. he said the valve body was bad and needed to be replaced. is it sheer coincidence that the CPS went bad and then the valve body failed? are these valve bodies really as crappy as everyone says? if so, should i not purchase a replacement from gm? not really sure what to do at this point? help me, please!!!!!!!!!!!!!!!!!!!!!