Transmission experts please advise on tow/haul mode.
 

I have a 2003 Sliverado 1500 5.3 with the 4l60e.
It shifts fine in normal mode but in tow/haul mode it sometime shifts harder then it should. I know it it supposed to shift harder in tow/haul to help with towing a load but when it shifts from 1st to 2nd it shifts so hard the truck shakes when it slams into gear.
Now I had the dealer take a look at it and their best transmission guy went for a ride with me and he said it was building to much pressure and shifting to high an RPM. He said this was caused form some kind of pressure valve or regulator(I forgot what he called it). He went on to say that this was not really a bad thing and acctually would help make the transmission last longer by getting nice solid shifts out of it and being easier on the clutches or something. I asked him if I should leave it like this and he said if it was his truck he would leave it but it was up to me and he could get it to shift smoother if I want . He said it was kind of like adding a shift kit to help get nice solid shifts instead of loose smooth ones.
Do you think he is blowing smoke up my butt? He said he has been working on transmissions for GM for 28 years and took the time to really explain how it worked so I think I believe him. I don't know much about transmissions so what do you guys think? Thank you!

Ya know, I read all that, but I still don't know if *you* WERE ACTUALLY
TOWING A LOAD OR NOT when you're talking about this happening. :)

I have a 2001 Astro ( :emb: but hey, its got all-wheel drive and I'm thinking
20 years from now the drivetrain would work great in a project car ) that also has the tow/haul mode, and I do
know it bangs some serious shifts in this mode without a load - but - I also
noticed reading in the owners manual where they pretty much said
yeah, it will do that, but put a load on it, and it will be fine.

If it does it while actually towing, I'd be worried.

I did not have a load on it when this happened.

Anyone else have any other input? Thanks!

When you add a load the shift will feel better. Sounds normal to me. When I build a trans. for a truck that works I get the same complaint and I tell them the same the same thing the GM builder told you.

Yah, when unloaded some of the shifts are brutal in tow/haul.

The thing I wonder about is that it did not this when new (has 14,000 miles on it now) and it only shifts hard fron 1st to 2nd and it is not consistant as sometimes it is smooth and sometimes it slams into gear.

Hard 1-2 shift?`
 

I would check computer for code P1870-converter slip code = computer failsafe - high pressure & resulting hard shifts, I recommend check generic mode on scanner as well as a code 1870 won't always set service engine soon light. clear codes and test drive again and see if problem goes away for awhile. PM me if you need some help, thanks for listening.......

Thanks Fastcat! It is at the dealer right now getting checked out so I will find out a little later what is going on. Do you know if I was to continue driving it in this condition would it damage the transmission(4l60e) or shortin it's life? I'll let you know what the dealer says.