I bought a 01 ram 1500 4x4 with the 5.2 and 145k miles, the truck had a bad trans so I got a 1998 ram 1500 4x4 5.9 parts truck. I did the sensor and harness swap into the older trans and put it in. I used the original 5.2 torque converter. The trans works fine but when I get to around 45mph or whenever it shifts in 3rd or 4th the truck will start shaking pretty bad. I found out if I leave it in 2nd gear it won't shake at all. Also when I do have it in drive and it starts shaking it'll go away if I let off the gas and if I give it more gas. I thinking that when it shifts up and goes to lower rpms the injectors aren't firing right but I'm not sure

 

That's a misfire. It's felt more in higher gears, and in O/D, with the torque converter locked, it can feel like the truck is going to shake itself apart. I have a look first at the tune up parts, Plugs wires, cap, rotor. Then take a peak down the throttle body, see any oil in there???

have a look at the be-all, end-all, plenum thread. Think its stickied at the top of this forum.

Welcome to DF.

 

A thing I've always heard is to unplug each injector one at a time to find a misfire and when I went through and unplugged each one it'd run different every time

 

On a fuel injected motor, that test is a bit different. Gotta get the engine fully warmed up, then unplug the IAC motor. Otherwise, the PCM will try and compensate for the dropped cylinder, and test results are questionable....

Also, if you have a decent OBDII reader, you can check misfire counters, and see what the numbers show. (as they are listed per cylinder. ) Easy to see which ones are bad. On a plenum problem, usually the rear cylinders are the ones that are problematic. And the plugs tend to get oil fouled back there as well.

Also, the test at idle isn't as accurate as you would like in this particular instance. That test is for a totally dead cylinder. Due to the nature of the plenum problem, it may idle perfectly, but, put it under load, and you get misfires. (lean-burn miss.)

We having fun yet?

 

Look at PENDING codes if it's not setting hard misfire codes.

Again, PENDING.

If none, keep driving it and TRY to make it happen then keep checking pending codes.

You have to be under high load (low RPM, heavy throttle) for these misfires to show up. That's why they go away in 2nd -- the gear reduction allows the engine to work less.