I have a 1999 jeep grand Cherokee larado V6.

2001 Grand Cherokee its under WJ series that run from 1999 at 2004; check in this link to download: jeep-wj-owners-manual-pdf.

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scan the trans look for govonor pressure & epc pressure

you should check the crank position sensor . The plug may need to be tightened up or its pins bent a bit to make a better connection. Has any other work been done recently?

check the crank sensor and the wiring

sounds like it time to have the front end balljoints inspected. Only with an inspection will you get the proper results. Why guess, this is a safety issue.

Code 1391 = An intermittant loss of CMP (crankshaft position sensor) or CKP (crankshaft position sensor. This code could be related to just a bad connection at either sensor or the wiring harness, check the connections and be sure they are clean and tight fitting with no loose wire connections also within the connector itself. Otherwise you may end up replacing one or both of theses sensors to correct this issue,unless you have an oscilloscope to isolate which sensor.

Right side of the engine block. A little off center towards the back. Should be sticking out the side of the engine with a plastic plug on a shaft about the thickness as a shovel handle.

Check for a bad pcm ground

First off, if you have a 2004 Grand Cherokee with the 4.0 liter 6 cylinder engine, then it is an inline 6 rather than a V-6. To answer your question, it has a timing chain.

Have you run an engine control system fault code test? If not do that first.