<TABLE class=tborder cellSpacing=0 cellPadding=6 width="100%" align=center border=0><TBODY><TR vAlign=top><TD class=alt1>When pulling a trailer yesterday I noticed my 05 lly did not want to pull it in overdrive (lost speed when shifted to overdrive) but 5 minutes before that it was pulling it no problem. so i just stayed in the gas just enough to keep it from downshifting and all of the sudden it was like someone flipped a switch and it started pulling great again. I do have a Predator running factory tune with speedo adjust for 285's. I checked for codes and it is showing P0101 I cleared the code and fired it back and the code popped up again and i did not even rev it up. Dealer sayes they will look at it next week. It does do it all the time it was just more noticeble under a load.
<!-- / message --></TD></TR><TR><TD class=alt2>http://www.dieselplace.com/forum/images/statusicon/user_online.gif </TD><TD class=alt1 align=right><!-- controls --></TD></TR></TBODY></TABLE>

There is a message from allison on the problems of gooing into 5th gear when you are towing and have 285's on it. I read it in another post, once i went to the link. I will do more research send you the link.

Q. Speedometer / Tires - What effects will big tires have on transmission operation?
A. The TCM calibration is based on factory tire size and rear axle ratio. Changing either of these parameters will have some adverse impact on transmission operation, including features like grade braking and shift stabilization. For instance, we have noted that when P285 tires are installed that the transmission generally does not shift to 5th range when towing heavy loads.


that is from this link

http://www.allisontransmission.com/service/faq/index.jsp?CategoryID=11

it is the frequently asked questions area Allison's website.

It did it before I changed tire size too

I really payed attention to it today and I think that it even does it in all the gears it but not every time. it is just more noticble in the higher gears when the motor actually gets a chance to work

You may have to place the original size tires on per this TSB.

http://dieselplace.com/forum/showthread.php?t=264

I think it sucks but your dealer may refuse to look at it, if they know about the TSB. I just stumbled on this earlier today.