Vehicle is a 4x4, also has 159,000 ish miles on it. Vehicle had plugs changed, starter fixed, new battery, all the general stuff done in December because it sat for a while. My check engine light has been going off, so we got a mechanic to look at it, diagnosed it as a cylinder that isn't working, so he says he will have to replace all cylinders to fix this....
Does this sound right? The truck does misfire some. What should this run to fix if it is the case? Could it be a simple issue that can be fixed easily that I can do by myself?

Does it miss at an idle? Only under a load? All the time? Just one cylinder?

Also, you dont "replace a cylinder" persay.

It misses at idle, haven't towed anything, and misses while driving. Mechanic said one cylinder didn't work at all.

Check plug, plug wires !

You need another mechanic. Plug wire, spark plug, injector are likely suspects. More details would help, like Alex K. asked. I am more of a Ford man, is this fuel injected or have a carb?

it could be a number of things, vacume leak, bad plug, bad plug wire, bad dist cap, low compression, burt intake or exhaust valve, ect.

best thing to do is start with the basic things, replace the plugs and get some good quality wires like ac delco and a new dist cap. if it still has the miss, run a compression test, if thats good (should be above 100 psi) then could be a injector. i think a 96 has the spider Assembly inside the intake. those was bad about crapping out.

what was the code making the light come on?

you need to have the truck checked out properly by someone who knows that setup well,as stated there are several things that can cause the misfire on that year model.And it will be cheaper to have it diagnosed properly before you start throwing parts at it.

The only thing you can really replace just 1 cylinder on is a diesel with a liner in it.

I would also ask for a compression test on the cylinder he says is bad.