Ok, here is the scenario, I made a long trip (600 miles) today, and I would be driving down the road with the cruise on, then for no reason, the tach would drop, speedo would drop, and cruise would shut off, but everything else was fine, truck still running, radio and heat work, but a drop in voltage like my alternator just quite putting out also. then I would have to shut the key off, let engine die, turn it back on with clutch in, turn key to start, and drive away normal. It would do this sometimes as often as every 10 minutes, then last over an hour just fine. I am not doing anything when it happens. Here is another wrench in the equation, if I just leave the truck in gear rolling, shut the key off, then back on, it will not fix it. I need the engine to shut off, and must push in clutch and restart with key. Any help would be appreciated.
Thank you,
Ryan

 

Check the engine speed sensor. It is down by the crank pulley on the front of the engine. Look for any chafing of the wires or a loose connection. I also have read something about the wires can get broken somewhere around the alternator too. The Engine speed sensor controls everything you said acts up.
Tom