non mopar truck problem need some help

[4aThrill]

For a while now I have noticed that my truck tends to slow down/drag when going down hills, instead of speeding up. I don't touch the brakes or anything like that to make this happen, it just does it. I have had the brakes checked there all great, the Transmission was checked today no codes came up and they said nothing is wrong. So now I am asking myself what it could be. The truck has 130 thousand miles on it and is paid for and is more than 10 years old, I don't plan to sell it anytime soon. I already bought one car for the wife and my other car is in the body/paint shop. So a new/used vehicle is kind of out of the question to get, rather fix this one got another 50 to 60 thousand to put on her. I know it's not my imagination because my gas mileage has dropped too. I was getting 14 around town now it's more like 11 and on the highway it's now like 14; used to be 16 or higher. I know the saying if it's not broke don't fix it but if it's making me spend more time at the pump; more often then usually. I would like to find the problem and fix it. I know that it's not the brakes or the transmission so could it be something up with the engine; any thoughts of what it maybe? 

[Tilar]

It's been many years since I worked on any automatic transmissions, and since you didn't post any make, model or year, this is on the SWAG system... But it sounds like you may have an overrunning clutch binding up in the transmission. And I doubt this would show up on any code test.

[4aThrill]

1995 GMC K1500 4x4

[1969chargerrtse]

Any chance you noticed lost of power while accelerating etc??  A clogged catalytic converter will drag a motor down and not bring up any codes, motor just can't breath.  Sometimes if you floor it while driving parallel to a wall or highway fencing you can hear the hiss of the tail pipes screamming, GIVE ME AIR!!  Just a thought.  Seen it before, stumps even the best garages because no codes show.   It'll run fine under normal circumstances, but under loads starts bogging or getting poor mileage,  yet if it's not to clogged, run fine under light driving, until it clogs further than it just drags the vehicle down all together and is easy to figure out.

[Tilar]

I would take it to a reputable transmission man and tell him what is happening. I'm still thinking the overrunning clutch is binding up somehow.

When you are going down hill and let off the gas pedal, Does the engine slow right down or does the engine feel like it is slowing the truck down?

[4aThrill]

the engine slows right down, I don't feel the engine really slowing the truck down. the catalytic converter is just over 6 years old had it looked at the outside of it, still solid but that does not really say anything. I do have some type of noise on that side of the truck from time to time a thud  or something of that nature. after the truck warms up and sitting at the light I will hear a nice little thud, i thought it was either the trans about 3 years ago or the converter but it still does this today with no change with the sound. So now I am thinking could this be also apart of the problem that I am having too? I would like to get this fixed soon gas milage is droping nice now got 130 for a half of tank to what I used to getting 200 going around town.  thankx for all your info

[1969chargerrtse]

Hmmm, I would go down a hill that slows it down, and while I'm sure it's slowing, pop it into neutral.  If it still drags, then it's anything related to movement and stopping, minus the motor.  Trani, steering, brakes, and that should be it.  Now listen to this, I noticed that when I rolled out of my driveway in reverse backing out of the garage in my Charger, it just didn't roll smooth?  It would seem to have a drag about it.  know what it was?  If I pointed my steering wheel dead center straight, the driver tire was straight, but the tire on the passenger side was pointed out.  Tire drag, my toe in/out was off.  That would also drag mileage down.  But I would do the first thing I mentioned about popping it into neutral and see what changes you feel.  Feel free to PM me and leave your number and you can explain in better detail and I'll try to help.  I had my own gagrage for 5 years and enjoy trying to solve the odd ones.  Actually this is what I do all day but with Elevators and escalators.  Rob.

[4aThrill]

Rob,

Thankx for the info I will try that next time I leave town or I find a hill

Nick