Hey guys, I am new here. I inherited my (recently deceased) step Dad's truck which has 2 issues I am hoping to get some guidance on.

It's a 2006 1500 SLT with the 4.7 Magnum V8. I am actually a chevy man. I've never owned or even driven a Dodge truck until now. So if I use some incorrect terms, please feel free to correct or poke fun at my expense.

Issue 1: The truck drove perfectly fine going back and forth to my Mom's helping her move. It's about a 20 mile drive. I made quite a few trips. She had described this issue to me but it never did it, until the last trip back home. Basically, while I was driving at around 55 mph, it suddenly downshifted (as if I had punched the gas to the floor). I let off the accelerator and it just slows down in the same gear. Eventually, it shifts back into the gear it should be in. Then it does it again, and it goes back and forth like this. I was trying to get it home so I babied it and tried to keep a steady speed. For the last few minutes of the drive, it seemed to settle down whatever it was doing and drove normally. When I pulled into my neighborhood, it had no issues shifting in lower gears. It seems to only happen at higher speeds. It almost feels like an incorrectly adjusted detent cable (older Chevrolets). Though I doubt it's anything like that since I am sure "passing gear" is activated via computer in these later models.

Issue 2: I do have a CEL with code P0499 which I know to be an issue with a vacuum valve related to the gas tank. I kinda doubt these 2 issues are connected, but like I said, I've never owned a Dodge and just want to relay everything I am seeing. I'll be replacing the valve for this situation soon (waiting for my Mom to get her secession papers done before I put any money into the truck).

I am mostly posting with regard to issue 1, the "shifting issue" as we've come to label it now. Was hoping to get some feedback on what I can check before I dump a lot of money into this thing. If it looks like it will be too much BS, I may just sell it and give Mom the money instead. Thanks in advance for any advice!

 

I would start with putting a tps on it.

 

Is the TPS a common failure point for these trucks?
A new symptom I noticed tonight, and verified with my Mom that this happened for them before also. Keep in mind that I drove the truck with no issues for several days. When the crazy shifting issue started, I noticed today that the cruise control no longer works either (it won't even come on now). This happened when my parents started having this problem also. The cruise worked fine until the shifting issue started. Come to think of it, I'm pretty sure the cruise control depends a lot on the TPS, so that is definitely something for me to check. Thanks 3rdgens4sell

 

Its common for a bad tps to make the trans lock and unlock the torque converter when at speeds over 50. Driving around town mine had no problem and just happened out of the blue. I say replace the tps bc its cheap and the easiest place to start.

 

My truck has 124,000 miles and started having some issues with the passing gear. I put Lucas transmission stop slip and it certainly made my shifts firmer and smoother, but the original issue was still there. I decided to clean the MAP sensor or whatever it is in the air intake. I cleaned the throttle body, too. Then I checked the spark plugs and found the original plugs all burned down to the porcelain! I replaced the plugs with new NGKs and problem solved! This thing is a beast now! No shifting issues either.

 

That's great! All of that was already done to my truck. It runs like a champ other than the shifting issue and cruise control going out. Some days I can go drive it and it shifts perfect and cruise works again. I'm going to replace the TPS this weekend just to rule that out and also the vacuum valve (gas tank pressure valve) that's causing the CEL.

 

Thought I would come back and post an update to this in case anyone else runs across the same problem. Replacing the TPS fixed the crazy shifting issues. It's running like a champ now. Also the cruise control started working again. The TPS was very simple to replace.
Only issue I have now is I still have the CEL with code P0499. I removed the vent valve (under the truck, near the gas tank) and check resistance. It measured at 8.4 ohms. I think from what I have read that is where it should be. But I am confused about checking the power. Does this only power up when you turn the key? Another thing, the wire that connects to this valve (2 wires), I can't tell where the other end leads to in the truck. It seems to feed into the engine wire harness. I have no idea where it leads so not sure how to check that other end for breaks or loose connection. My truck is a 2006 with the 4.7. Can anyone tell me where this wire leads or what else to check? I'm at a loss. Inspection sticker expires this month (June).