My van has started hesitating when at a stop light or a complete stop what can cause this to happen

Without AC on..... the vehicle is ok at stop light? If so, sounds as if the idle is too low with AC on causing the extra load on the engine. Is the vehicle in a good state of tune ( spar plugs etc )? The throttle plate may be dirty causing minumum idle spec to be off. Inspect throttle plate and clean a necessary and retest. There may also be a problem with the idle control motor or a problem with vacuum leaks causing this issue

Transmissions work on clutches and clutches wear out. The wear is to the point that it cannot overcome the resistance when the vehicle is on the ground. It is time for an overhaul.

have you had the battery checked to make sure it is holding charge if this is ok check the alternator charge rate

If the check engine light is still on, It will have to be scran in order<To find out what cause it to come on, You can,t just guess what the (Problem) Is.

lol everything but the actual cause of the problem. The big clue here is your gauges. What sensor going bad will cause the gauges to jump? Ask your mechanic that wasted all your money replacing good sensors. Then you may want to find a good mechanic. The problem is a wiring problem. Probably the main hotline running from the ignition to the fuse block. Somewhere in that area. If you have the spark circuit on a scope you would find it flat line when it hesitates.
I dont think it is a short because if it was you would have blown fuses or smoke and or electrical smell. So it has to be an open circuit that would be nearly impossible to find. If I was going to just start replacing things, I would start with the ignition switch and then the fuse block and then any hot wires to and from both elements.

Have you found out what cause the problem, because the same exact thing happened to my van yesterday, and its a 1999 Ford Windstar also.

tsb remove dist cap ,clean out breather holes i replaced cap and rotor at the same time. chevy has the problem with the 4.3l astro,s and blazer i have both.fixed the problem when buying the cap and rotor the directions inside will also tell you how to fix

Also check all of your grounds, a little corrosion caused the same problem on mine. Just had to find the right ground. Mine was on front under pass headlight causing mine. Good Luck

I cannot see how adding a fuel additive would help to be honest. I would be looking for a split or leaking vacuum line, I have even seen a leaking evap canister before that caused a similar problem. Does the engine pull clean and strong when it is warm or at cruising speeds? Does it feel like its running lean or misfiring?