Will a exhaust header from a 2.3 fit a 2.5, I have a '99 with a 2.5, but cannot find a header for it. Any help is greatly appreciated.

 

If it is for a 2.3l Lima engine then yes
2.3l and 2.5l Lima engines used the same heads, 2.5l had a longer stroke

2.3l Duratec(2001-2012 Ranger) will not fit

You currently have mid-band "headers" as stock Ranger exhaust

Headers come in 3 "flavors"
Low-band
mid-band
high-band

A header works by using exhaust velocity to create a lower pressure at the unopened exhaust valves, so when that exhaust valve opens exhaust is PULLED out leaving more power on the piston because it doesn't have to PUSH exhaust out
The length and size of smaller exhaust pipes(at the head) and the size of Collector(large single pipe) sets where in the RPM band the lowest pressure will occur, low, middle or high
And thats were the free extra power comes from, scavenged power.

If you want better low end power then you get a header "tuned" for low-band
If you Race and want more power at higher RPMs then go with high-band tune
You already have mid-band

 

Going on a street driven truck which type would you recommend and manufactured by who.

 

I mean, I rarely get about 2,000 RPM during regular driving.

 

You get best power at 2,500rpm so should be running between 2,000-3,000rpm

2.3l performance info here: Ford 2.3L Performance - Route 66 Hot Rod High

Specs and history here: The Ford Ranger 4-Cylinder Motors - The Ranger Station