92 Speedometer

I need help. When my speedmeter showed 80mph, a lot of people passes me on freeway. So, I felt it couldn't be 80mph. So, with my friend's 2002 Toyota I follow him and asked him to drive at 75mph (well, speed limit is 65mph). Surprise! My 92 pathfinder was showing 83 mph. Also, my odometer rolls greater than it is supposed be (I used little mile sign on free way as a refference).

I have stock rims, & stock correct size tires. How can I fix this? Is it speedmeter it self or speedmeter cable, or what could it be?

Please help.

Thank very much.

My bet was speed pinion gear. I replaced it, no help. Please give me suggestions.
Thanks.

My 92 is 5-6 miles off too, I go 71 on the speedo and it's actually 65. The best guess of all sources I have talked with is the tranny was replaced and it effects the overall output to the speedo. So I tested the difference at all speeds and it is closer the slower and further the faster I go. (GPS helped in this matter) So basically I have to live with it... I suggest to do the same so you have an accurate idea on the real speed.

Bingo! I bought a whole low mile used instrument cluster and replaced. It fix the problem. My speed meter or speed sensor was not right.