It feels like it is missing when driving at a constant speed 45 ,55 & 65mph. accelerates great. Idles a little rough. have not noticed the problem when accelerating or decelerating. could it be egr valve or transmission modulator valve. I have done a complete electronic tune up. Replaced air and fuel filters.

SOURCE: Blazer runs rough when running at 45 to 55 mph

the problem was low transmission fluid. added half a quart and the problem went away.

SOURCE: 1994 ford ranger extended cab 6 cyl fuel injected 2 wheel drive automatic

This year of ranger had a few flaws, In one case, a break power booster was robbing the vacumm, you can test this by plugging it off and seeing the differance, but you will have limited brakes. This model year had a problem with a vacuum leak on the manifold. You can check these in many ways, but please don't use starting fluid. The rear of the manifold usually on the drivers side where it seals to the block.
Also, in 2 other cases a cracked head has gave me the same problem. It is caused from a loss of vacuum.

SOURCE: 1996 FORD CONTOUR 4CYL ROUGH IDLE ROUGH ACCELERATION

no problem. If you are getting that low of voltage on a load then you might want to test the alternator as well to make sure it is running at capacity.

SOURCE: 93 toyota pickup 22 re motor, idles very rough

it is possible.

SOURCE: 1996 Jeep Laredo shakes between 55 and 65mph

worn or loose wheel bearings-tires out of balance-worn tie rods-worn ball joints -rotor has high and low spots.