2002 chevy 3500 wont shift out of 2nd

I have a 2002 chevy 3500 with a 6.0 and 4l80E transmission 4x4 dually. I replaced the rear main and when I put the trans back in it would not shift out of second. I dropped the trans pan and found the 1-2 shift soleniod to be bad. After replacing the rear main seal, The transmission would not shift out of second gear I replaced the shift solenoid and this helped it to shift properly except when you are going down the road the engine starts to miss or load up and shutter when the transmission tries to shift into ovewrdrive