'98 5.7 Terrible Gas Mileage

[Bclem]

I was leaking coolant on my 98 silverado 5.7. I could not find the location of leak, it was on the passanger side, back of engine. I replaced the intake manifold. No leak now. Truck started with SES light on. I had the code read at Autozone. It was cam/crank correltion. From reading the forum I learned that the distributor was not put back exactly right. I moved it one increment at a time, now the light is off. Here is the new problem. That was 400 miles ago, now I get about 8 mpg in town and 10 mpg on highway. Also truck seems like there is no power going up hill. 105K miles on truck. One more thing to add, until 3 weeks ago I only drove this truck 3 miles per day, to and from work only. A few years ago when i drove it all the time it got about 15 mpg. Please let me know your thoughts. Thanks