Truck doesn't like to downshift?????
 

Hey guys. I've got a 2003 1500 5.7 with an automatic transmission and like the title says, it doesn't like to downshift. It seems to do it the most when I'm in 4th gear. If I put the pedal to the floor it just stays in 4th and won't downshift to 3rd. I either have to shift it manually on the column to get it to downshift or repeatedly push the pedal to the floor and back. It hasn't thrown any codes either.

Also, I've noticed that it seems to be getting real sluggish. For example if I'm cruising down the freeway at 75 mph with any kind of a head wind it will not hold speed in OD. A few weeks ago I was hauling a fridge and it would not hold 70 mph in OD down the freeway. I had to drive all the way home with the OD off.

I don't know if I'm just imagining things but I didn't used to have any problems zipping down the freeway or hauling light loads. I used to be able to haul a 2 place snowmobile trailer with 2 sleds on it in OD at 70 mph no problem.

I read a thread on here where a guy was having similar symptoms and ended up replacing the MAP sensor to fix it. The big difference between his symptoms and mine is I'm not throwing any codes. What do you all think is going on? Could it be the MAP sensor even though I don't have any codes? Thanks!

When is the last time you did a tune-up? The spark plugs are due every 30kmi so you could be losing some performance right there.
Also, when is the last time the transmission fluid was changed/flushed and filters changed? Your fluid should be completely flushed at 60kmi and filters changed at 100kmi or there abouts.
Also, these trucks are notorious for flooring the gas in order for the trans to downshift. That was the first issue I noticed with mine and I purchased a SC tuner to improve on that. You cannot do anything since yours is an '03.

I would do some maintenance and see if that doesn't help you out some.
Hauling a fridge that is standing up is a brick wall for the air, so it doesn't surprise me that you had a hard time staying in gear.

Hey Dirtydog, thanks for the pointers. I replaced the plugs about a year ago. Maybe I'll have to pull them out and see what they look like. The trannny was flushed about 20k ago when I bought the truck. I have about 85k on it now. The weird thing is even when I push the pedal to the floor and hold it there it won't shift down. Like I mentioned in the first post I either have to repeatedly push the pedal to the floor and let it out or use the shifter on the column to get it to drop a gear.

I would clean your throttle body as well. could be gunked up restricting flow and opening of the plate.

Also, with the intake tube off, have someone push the pedal to the floor and make sure the throttle body plate has full range of motion, meaning at WOT, make sure it's all the way open.

How is your gas mileage? if it's below 10city/15highway, your 02 sensors could be of culprit even though your not throwing codes.

I've been meaning to get to the throttle body so I gues now is as good as anytime. I've been averaging 12-13 mpg with city and highway driving (mostly city.) Is there a way to check the 02 sensors or do I just replace them? Thanks again!

Supposedly you could use tuner to read the milli-voltage on the O2s to determine if they are good or bad. i forget where the thread on how to do that is though. New O2s arent but about $25 each though.