You haven't said what you budget would be so it's an unknown approach but since gas mileage is a concern, you have Chicago winters, and probably want an automatic I'd consider the stock S10 drive train. The 4.3 S10's came with 700R4 overdrive transmissions. No matter which engine you choose it will need to have fuel injection with all the sensors to get good mileage, carbed engines just won't equal injected engines in that department and they are good cold weather starters. 5.4 or smaller engine, OD trans, and a rear end that will make around a 2.75 final gearing would be a reasonable target. If a shop furnishes the S10, AD Engineering kit, engine, trans, rear, exhaust,plumbing etc.,you can expect conversion bill of around $12-15k. Once the conversion is done you will need a modern fresh air heater or heat-A/C to keep the windows clear enough for winter driving. These were 45-50 mph trucks on roads that were mostly only good for that speed so when driven 70 they have wind noise you won't believe and there is NOTHING you can do about it without investing cubic money. They have no seat belts and the door latches are a joke which once again can be cured with $$$'s. If one has a shop and can do much of the work then a truck like this is not out of reach but if one has to pay for everything then $25-30k can be expected.
