170K 4L60E Harsh 1-2 upshift.

[99Vortec]

Yea, fluid level is good. No leaks from either transmission or transfer case.

Nasty front pinion seal leak going on though.

 

[SunlitComet]

then i would look into the valve body fix.

 

[Donnie Yukonie]

I'd replace the trans

 

[livingez_123]

A simple spring in the valve body will fix the 1870 code issue. any rebuilder doing a 4L60e would address it..... if not, find another rebuilder.

 

[99Vortec]

I forgot to mention that the problem has not resurfaced since replacing the throttle position sensor.