Have noticed more and more how much nurturing the truck needs from cold. It used to be just a few seconds with a little throttle and then it would idle nicely. Now it's 5 mins and when the temp needle just about swings past the C it doesn't like idling at all. Then once it's warm it still doesn't want to tick over for the first mile of stop start driving! Not only that but the damned oil light flickers on tickover to the rhythm of the pistons when its warm. WTH!!! So please guys, help. It couldn't have started going so wrong at a worse time.

God forsaken V6 3.8 Essex lump......I hate it. Just been laid off work though so can't go throwing money at it, V8 plans shelved for the moment.

 

Just my 2cents here. Change the oil if you haven't recently. You may be watching the effects of thinned oil at low (ruff) RPMs. From the sounds of things to me it may be a cold temperature enrichment issue. If its carbed, then check the choke top to bottom. If the choke is electric, it could be dead. The small heating pill as its sometimes called, could have given up. This could cause the rig to do all you mention and more. Such as letting the choke start to close during warm use as well, with a resultant oil thinning and black soot inside tail pipe(should be grey after a good drive).
If the rig is EFI? you could have a bad censor. Intakes of all kinds have em so check yours for vac. leaks and or prop per electrical connections. Your 83 should have a bymetal intake temp. vacuum diverter in the stock air cleaner, you can check its operation with a hair dryer and some spare vac. tube.
With all the mods listed to your sig. I would guess the engine isn't bone stock? Is that the case? If its not though my suggestion of looking over the choke real good still applies. If the rig has electric lead going to the carb then you may very well have a bad choke cap heating unit. I've seen a choke open as it should, only slower, with a bad cap and then start to re-close as Engine RPMs increase. Because the air that flows through the choke area becomes cooler. My once stock, 83 351 had a choke stove. They are notorious for burning through inside the manifold and allowing exhaust to be ingested by the choke. So if that applies check it , they can plug, as well ( they where used instead of electric in some cases).
All that said, Timing and plugs all in good shape? If you find the choke to be faulty, its a good idea to clean, file , and re-gap the plugs for good measure. It shouldn't cost a bundle to fix if you find it soon.
I have that 3.8 in a T-Bird (87) and it does the same oil light trick with only a couple thou. on a oil change. Its CFI not carbed. The oil pumps sitting in the aluminum timing cover. Not fords brightest moment. The timing cover, has to be replaced with pump gears for hefty big bucks, in many cases.
Best wishes.

 

Damn I should have said, it's carbed. Have all the necessary service items on order too. Will do as you say.

 

Hope it helps. Carbs an I, tend to get along pretty well. I will miss em when every thing goes Injected. Please don't get me wrong though. Injection is pretty much the best way to go, at any rate. Ill just miss the comfort zone.
That Slime GREEN is pretty rare. Each rig Ive seen that color really catches the eye. Not the most appealing maybe, but an eye catcher none the less.
Good luck with it.