How often has this engine been run?

It could possibly be stuck rings,, longshot I know but it will either be stuck rings or just plain worn out.
A rebuild is is due if you want to have a dependable truck,,, OR see what you can do with a cylinder hone, new rings & gaskets and a AAA towing subscription eek grin

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
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Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!