Diagnosing Slow Acceleration In New To Me Truck

Isaiah Estrada

Active Member
FCBO Gold Member
Jan 20, 2020
Reaction score
Santa Maria, CA
I’ve been tired of keeping up with the payments and upkeep of the newer Silverado I’ve had for almost 2 years. Decided to bite the bullet and sell it. Wised up and bought a Dodge yesterday! She’s a 01 Ram Laramie SLT. 5.9 Magnum, 3.21 rear. Not sure if it’s the 42re or 46re trans.

I know this is the C Body forum BUT, you are all my wisest advisors… Truck is relatively clean for the year. It’s got 127,000 on the clock. Sits just below 40 psi oil pressure at idle (maybe about 35-37-ish) and builds up to over 50 while cruising. She purrs like a kitten and drives amazingly well around town!

However, I notice a loss of power on the freeway. I usually remedy this by turning off the OD and she will pick up where she needs to. Still, I fill like I’m flooring it to make it keep up. I’m wondering if this is potentially ignition related or fuel delivery? I’ve also heard of clogged catalytic converters causing similar issues. Mainly uphill inclines cause this 5.9 to struggle. Which surprises me, as for one - she’s a MOPAR and 2, my old 4.3 V6 Silverado that was the same age didn’t struggle as bad as this 5.9 does. Anyone ever own one of these trucks and experience the same thing?

Looking forward to putting the money I save with this paid off truck towards my New Yorker. It’s been far too long…


own a scan tool? any fuel or cat issues would set codes. cat efficiency and fuel trim. we did one recently that had a bad O2 sensor on the drivers side that ran that bank full lean. also had leaking intake gaskets. if the truck sat a lot you could check the air cleaner for a mouse nest. that's a common problem around here that won't necessarily set a code. nice little truck though.
Last edited:
5.9 will always be paired with the 727-based 46x trans. You'll have the 46RE.
3.21 gears and those tall tires isn't helping.
As @rags mentioned, the intake plenum gaskets are prone to leaking, that can cause oil consumption and detonation when the oil gets sucked into the cylinders.
A weak fuel pump could contribute to reduced power, as could something plugging the exhaust.
Even if it's just a tiny gasket leak? Or where the gasket is puckered out between the bolts?
Asking because I've never had to diagnose one.
I've got nearly the identical truck (purchased new) with the exception that mine is a 2500 4x4 and has 4.10 gears, but only 88K miles.

My guess is that 3.21 gear paired with larger tires is causing most if not all of your problems.

As far as code scanning, you can do that with the ignition switch. Cycle On/Off/ 3 times in succession within about 10 or 15 seconds (without starting the engine of course) this will show you any codes on your odometer display. Of course, the check engine light will be on too if any codes are present. I would think you should have the 46RE transmission, but being yours is a 1500, maybe it is a 44RE?

If it was an intake leak, I would think that it wouldn't idle well, but you have stated that it runs well.

Being that you got the truck used, you probably do not know the prior history of it, such as whether or not it has seen a lot of towing. I did quite a bit of trailer towing with mine and at 75K miles the 46RE flat out quit on me. It was probably fine until I got the second trailer (enclosed vs previously open) and the increased load from wind resistance is what I think took it out. So what I'm saying is if previous owner towed with it, the transmission may be worn and slipping at highway speeds.
A transmission that slips during shifts might last awhile if it's babied.
A transmission that's slipping constantly at highway speed is going to toast the clutch or band in short order.
It's because these trucks weigh like 5500# and are being driven by a small block. The OD is like .69:1. They are in reality a poorly designed driveline. I don't know for sure, but I would assume they got govt/EPA credits toward mpg for window sticker.
1. You are never getting more than 12-13 mpg's out of one of these pigs, my old '77 square body Chevy got that
2. I cannot believe that the power train engineering group could screw the pooch so bad, remember this is before the Germans invaded the company and drove off the talent. So there has to be a better reason than bad engineering.
3. Best thing you can do is change the gears. I know it's a lot of work, but it really is the only way to make the truck drivable. Around here mother nature and overzealous salt truck drivers would have dissolved the problem prior to this date. In So.Cal you could theoretically drive it for another 30-50 years so a $1500 lay out seems prudent against a $70k new truck that it's computer will kill the truck long before 30 years.
Sometimes I'm glad to realize I do not have that many years left on the planet.