i have a 1992 ford ranger xlt 2.9L 5sp standard. gears 1-3 are fine. however 4and 5th gear a problem. at 45mph i'll put in to 4th gear and it loses power and shakes/sputters. also in 5th gear. acts like a mis-fire. i changed: plugs/wires, egnition coil, fuel pump/filter/sending unit and fuel pump plug. what's wrong.

When you shift into 4th girl and it loses power it sounds like your loosing pressure. Check your fluid. Make sure it is filled and clean. Here is a link to a forum where someone had a similar problem. I would read through it, it might be helpful: http://www.automotiveforums.com/vbulletin/t285782.html

the transmission in you truck is famous for losing 5th gear they break very frequently, does if it grinds or makes a bad noise in those gears it could be broken teeth or shot bearings.

i had a 84 bronco 2 with the same problem and i had to change the clutch, pressure plate, and throw out bearing. but it comes as a kit if you get it from a parts place like autozone or advance auto parts.

sounds like your tranny is fine,have the cat converter checked,it may be cloged up.I say this because you looseing power in 4th,5th is like overdrive.also try a bottle of fuel injection cleaner in a tank of gas,may be dirty injectors,sea fome is best.

another item to check is the speed sensor on the rear axle. my 99 did that and the problem was the speed sensor goin bad. once it was replaced everything worked well. the speed sensor works with the computer and tells the engine when to accelerate. I know 95 and newer rangers have this speed sensor for manual and automatic tranny's not sure about your 92.