My '01 Ranger just had the spark plugs reinstalled (I tried to install them myself and was getting rough idle). Apparently they were seized when the shop commented on the rough idle after inspection. They recommended removing and rethreading the spark plug threads which they did(for a hefty fee...). This is the second time I have taken it to this particular shop.

The first time I took it to them was for a cracked radiator fan with new clutch and afterwards had the same problem - which... brings me to the issue I am currently facing.

Going uphill - like an onramp to the freeway going 55mph the truck begins to hesitate and jerk like it wants to shift up but can't. It only does this going uphill around 40-55mph. Haven't taken it on the freeway but I'm pretty sure its just having trouble with the shift from 4th to 5th. It's an auto tranny btw.

The first time that I took it to this shop was for the Radiator fan and clutch. I had the same issue.
It came up with a check engine light which scanned as TPS Sensor. I disconnected and reconnected the plug and after that it ran fine. This was last month.

Now, a month later, after new plugs and wires I get no codes, just the bucking in 4th to 5th. If there are any threads or advice you could give I would be all ears.

 

First thing would be to change the fuel filter, its cheap and not hard to do
If you can get a fuel pressure gauge and a vacuum gauge I would test fuel pressure, raise RPMs to 2,5000 and hold it there and see if pressure starts to drop, if so(assuming new filter is installed) then fuel pump is starting to fail, or regulator, but both are on the fuel pump assembly

Hook up vacuum gauge to intake manifold, start engine
Should see 18-21" of vacuum, assuming elevation is under 2,000ft
Now open throttle wide and then left it snapped closed, should see drop to 0-2" and then recovery to 25" as it snaps closed then back to previous 18-21"
Slow recovery means exhaust may be partially blocked

Then raise rpm to 2,000 and hold it there, vacuum will drop and then come back up, if it start to slowly drop again then exhaust is plugged up

 

Thanks
I installed the new fuel filter. Still doing the same thing. I think I'm just going to take it back to the shop when they open and have them test drive it uphill on the freeway to see what I mean. I don't think that they did a very good test drive last time.

I have no access to those gauges and can't afford to rent any. At least I can get around town okay and I have a new Fuel Filter installed

 

I decided not to take it back to that shop after all. I tried checking the transmission fluid levels and it looks high.
Just got back from the 20 mile drive and checked the dipstick and it read kind of a faint liquid over the crosshatched areas about a half inch.

I added Mercon V (auto tranny) about 3 months ago and have never noticed a thing since this shop messed up my 3rd and 4th gears with their spark plug re-installation. They said that something could have gotten into the engine when they tapped the cylinders so are there any cylinders I should re-check? Or just rent the fuel pressure gauge?

I'm at a loss now....
It's not as noticeable but if I'm going uphill or have A/C on it is definitely having a hard time shifting from 3rd to 4th. Should I check a certain cylinder on the V6 SOHC?

 

Had to wait 2 weeks for free diagnostic at a local transmission shop.
Scanner read misfire on cylinder 1.

Put original plug in - issue resolved!

 

Good stuff

Thanks for the update