Does anyone know how to trouble shoot this, after climbing from 1500ft to 3000ft, i pull onto a side road, my idle and oil pressure then drops, and then finally stalls. after a 20 seconds, i restart, runs a little rough, but gets me the rest of the way, with less that 100% of normal power. Could my alda be misbehaving?

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'80 300SD - 315,xxx miles,
'79 300SD - 199,xxx miles