My 1993 Ford Ranger 4x4 has a problem with cutting out at highways speeds. The problem usually starts at about 70mph.
I figured it's a fuel problem so i have changed the fuel filter, that did't help, so i added some techron injector cleaner and that worked for a short period of time. Do you have any advice or have you heard of this problem?

 

Look into the fuel control unit. I have heard that it was set at the factory to either cut the fuel flow above a certain speed or at a certain rmp to prevent overspeeding. Could be faulty. Thats all I know, Im researching it myself as I have a 94 ranger splash.

 

Welcome both of you to Ford Truck Enthusiasts!

I know that my '98 4.0L Ranger has both a rev limiter and a speed limiter. If I try to go over 94 MPH or rev higher than 5200 RPMs (each number approximate) the PCM will start to shut down the fuel injectors and my motor will begin "limp" until the numbers are brought back down below the thresholds.

Unless you are winding out your engine and the RPMs are racing way over 5K, I doubt that's your cause. (If I recall correctly the 3.0L vulcan redlines at 5500 RPM).

Also, 70 MPH seems a bit low for the speed limter to be kicking in.

I assume your engine is running at WOT when your going 70 MPH, so it might be an air intake or throttle body-related issue. Have you cleaned them lately? What about a new air filter?