loose power on high end

[dmigura]

This may not be the right forum to post this question, but this is where i always go. I have a 1970 4x4 with 71,000 miles original motor. I have had about a year and it looses power at about 65mph especially when I am going into the wind. the motor also starts to clatter a little. I replaced fuel filter, checked timing, and run medium otcane fuel and still the problem exist. Any ideas on what it might be.