Hey guys random question, so I have a 03 4.0 ranger with a 5 speed in it, and the past couple days I’ve been hauling a wood chipper around with it for work, lots of highway driving (Barely feel it when driving around) and yesterday I was ripping down the highway at 120/30 with no problems at all, yet this rainy morning I hop in and on the way to a job site, I can’t really get over 110km/h on the highway in 5th, it’ll get there but takes forever with the gas on the floor but if I drop it down to 4th I can get there no problem, am I just overthinking this?

 

2003 4.0l SOHC makes best torque at 3,000rpm
This means to have any power RPMs need to be between 2,500-3,500

So whats your RPM in 4th and 5th at 110kph?
This depends on rear axle ratio and tire diameter

And just as an FYI, humidity reduces engine efficiency and performance with it
The MAF sensor is used to WEIGH the air coming in, it uses a heated wire, the more the wire cools off the denser the air so the heavier the air so the more Oxygen it has.........
Well with humid air its less dense but MAF reads it as dense, lol
Its a small difference but can be noticed in some situations

 

4.10 with 31s, it’s a pretty much stock FX4, in 4th it got up to just under 4 thousand rpm and in 5th it stayed under 3 the whole time it didn’t feel any different it just didn’t have the go I’m used to it having

 

Could be a couple of things
When did you last get gasoline?

The 4.0l SOHC runs 9.7:1 compression ratio so can't run Regular gas(87 octane) as is, it would ping/knock like crazy
So Ford uses a Knock sensor which allows the use of 87 octane fuel
But it means less power, because of the changes to spark advance
If you got some lower octane fuel it would mean even less power
You could try adding a few gallons of 93 octane to the tank

You can get Bluetooth OBD2 readers that can show you real time data while driving, usually under $25, you need a smartphone running a free APP or $5 APP(for more info)
These work on any vehicle sold in US or Canada since 1996, so good tool to have in any case
You could then watch spark advance changes, and fuel trims


Exhaust flow
You can use a vacuum gauge to test for exhaust flow and incoming air flow issues
Long shot but not a no shot, lol