Hard 1-2 shifts when towing

[willxfs]

I have a ’98 2 door, 4wd with 225,000 miles. Engine and transmission are original. I get hard shifts from 1st to 2nd gear only after I have been towing something for at least an hour or so. All other gear shifts are fine. When I’m not towing anything, it always shifts fine and never skips a beat. A long while back when towing, the service engine light came on. The code was P1870, I think. When I researched the code, it was something do with the transmission reaching or exceeding maximum line pressure. I’ve read that overhauling the transmission valve body and/or installing a shift kit may solve this problem. Seeing the high mileage that I have, should I even bother with the quick fix or just bite the bullet and get the whole transmission rebuilt. I plan on keeping the truck for a long time to come. I just bought a boat and will be towing about 3500 lbs. fairly often. Thanks

 

[retorq]

Get a new tranny or rebuild that one and get a huge cooler.

 

[letsbangout]

I also have the hard 1-to-2 problem that you do, but mine is intermittent and can't be linked to towing or anything really, except (anecdotally) to bad post-cat O2 sensors. I get a P0141 frequently and when the SES light is illuminated, the problem is worse. When it isn't, the problem is more intermittent. Either way I don't think it's a valve body in my case. I'll be replacing the O2 sensors shortly. I'm also suspect of the throttle position sensor, which plays a huge role in how the tranny shifts. I'll be taking a look at the linearity of its output with an analog meter in the not-too-distant future also.

In your case, I'm not so quick to suspect the valve body, but something's definitely going on. Does your fluid look off-color (dark red, or closer to brown) or smell burnt?

---------- Post added at 03:04 PM ---------- Previous post was at 02:53 PM ----------

FYI, the GM Technical Service Bulletin related to this is: http://www.gmtruckhq.com/drivetrain/gm-service-bulletin-about-code-p1870-1578.html

 

[SunlitComet]

Get it overhauled and incorporate the design changes and you will be fine. It is a valve body related issue that will get resolved during a proper overhaul that incorporates improvements thru the years.

 

[Gzes]

Well mine didnt do that but one day it went clunk and boom blown transmission. I would get it overhauled before it happens to u. By the way it will save u from where u need to be quickly andthe problems with the stupid tow trucks

 

[ezdaar]

When you blow it up. Look here. Remanufactured performance trans.

Or here for a brand new trans

 

[willxfs]

Thanks for the comments guys. Looks like it will be $2500 for a new/rebuilt tranny. I suspected this would be the way to go. I guess I'm doing pretty good to get 225k miles on the one I have. It was well cared for with the fluid changed every 50 or 60K miles. Right now the fluid was changed a couple of years ago with probably 60k miles on it and it still looks good. Probably going to get the Level 2 Raptor from PACT Transmissions. Can be seen in the following like. What do ya'll think?

http://www.transmissioncenter.net/4l60e.htm