Is there any usual "rolling resistance", i.e. if you put it in Neutral and let it roll on flat ground do you notice any drag causing it to stop rolling?
Vacuum gauge costs about $25, very handy tool to have around
Good read on how to use it and what info can be leaned: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine
Specifically you want good high vacuum at idle, it means good compression and no leaks.
And then you can test for clogged exhaust, exhaust restriction really lowers engine power.
If Vacuum tests out as OK then I would rent/get a fuel pressure gauge, 2000 Ranger is a Returnless system so fuel pressure should be 65-70psi even at higher RPMs
If yours is under 40psi then you would have a lack of power BUT(big but) you would also most likely get a Lean Code and Check Engine Light(CEL)