Just picked up a 94 ranger 4x4 5speed. 4cyl. Took it out on highway and had a hard time keeping at 65mph i it has 31inch tires on it and was thinking that may be the issue .any thoughts

 

It should do better than 6mph even with 31's on it.

 

Yes, I think the tall tires are a very likely cause, considering you have a 4-cyl. The stock tire height was probably in the range of 27-28 inches. I think my '91 4.0 came with 215/75-15's.

 

sorry, I had a typo, I am having a hard time keeping it at 65mph, I suspect the tires are to big, going to look for stock size. runs great other wise

 

I'll second that. I've had a '94 2.3L for going on 11 years now and they're slow; even with the stock tires. 93truck, have you checked your speedometer against a GPS system? If the speedo wasn't adjusted after the larger tires were put on it could be giving you a lower reading than the speed you're actually going. The tires could be a double edged sword so to speak.

Josh

 

Have you checked to see if you have too much play in your accelerator cable? If you do, the throttle isn't opening far enough, and you'll be pushing the accelerator hard as can be and still not getting any power. Check up under the dash where the cable attaches to the accelerator peddle. Take out any slack with a small wire cable clamp or something similar. It will make an amazing difference.

 

You are way undergeared with 31" tires. Stock tires are probably in the 24 1/2" diameter range and the 31's are typically in the 30.5" diameter range per Tire Rack's chart. That's almost 20% circumference difference if I still remember my grade school math.
Does it hold 65 in a lower gear?