Help? 98 Lincoln Mark vii dies when slowing down or stopping after being on the road for an hour or so,

Not that complicated- only two components have that type of failure/symptom. There are no cam or crank sensors on your '89 302 v8. The ignition module mounted to the side of your distributor is the most likely culprit. Check for spark when it won't start. No spark = the ignition module isn't tripping the coil. Because of the design of that module (Schmitt Switch and Darlington Amplifier), the duty cycle on the coil is very near 99%. Lots of current and lots of heat for a long time in the module cause it to shut down. If your vehicle has spark but still won't start, check the fuel pressure. Simply pressing the schrader valve on the fuel rail will spurt fuel but won't indicate it's volume and / or pressure. You need a gauge. BTW - neither failure will trip a code or a check engine light on this old EECIV / OBD1 system.