Got a 74 chevy C-10 with a 10 bolt rearend on a th350. rpms are high at 50mph does this mean i have high gears. not for sure of ratio

how high is high?

4:10 not so common
3:73 most common
3:08 found in the 305 AT trucks

The lower the rear end gears(higher numerically) the higher the rpm at a given mph. If you have a tach and know the tire height one can use an online calculator to get an idea of what the rear end ratio is.

My '74 has 3.42's. It was originally a 'three on the tree' 3 speed manual. One sure way is to pull the diff cover and look for the numbers on the edge of the ring gear, or do some counting.

It's odd to see a 10 bolt in a '74... Are you sure of the year? You may want to count the cover bolts again. This is irrelevant to ratios, though.

The rearend is definitly a 10 bolt. I've been told its a 3:73 but I want to be 100%. But she definitly has high rpm doing 50 on the interstate(higher than usual).

Jack up one rear wheel.

Put a chalk mark on the bottom of the tire & mark the driveway at that spot. Also put a chalk mark on the driveshaft.

Now rotate the tire TWO exact turns while counting how many times the driveshaff turns. A 373 ratio will make the driveshaft turn 3 & 3/4 turns. A 307 would be a little more than 3 turns, but not near 3 & 1/4 turns.

My 1978 K-1500 GMC had 3.55's from the factory, it's still got them and worked great with 31 inch tires.

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