I bought new long bock from Chevy house and the truck is stock. I'm looking for the best performance and gas mileage possible for 1500 to 2000. can you help me out I want power and gas mileage is it possible  

I want power and ability but without saying what exactly these things are it's difficult to determine what I'm after...  

Need more engine information, heads, cam specs, etc. Then we can see what we can do with what you already have.  WIEDER  

I have '90 chevy 1500 truck and it runs power enough and better gas mileage. I try to keep it at same gas mileage while I added some parts that make it more power. I have it overbored .030 with 2 relief flat pistons for better compression but since u got new block, stay with it. I changed cam to mild performance. I learned that the stock cam was .390/.420 in '90 engine so i upgraded to .420/.442 to keep at low performance. Also replaced weak valve springs with new z28 springs in heads. The swirled spacer and riser plate was added to tbi for better torque, of course tbi needs to be cleaned inside and outside. Replaced stock coil with MSD coil and better spark plugs wires. U can order underpulleys for crank, water, and alternator and u wud get more than 10 hp and doesnt affect gas at all! Also, with new headers that can replace stock to fit same exhaust pipes, no needed cut or weld pipes. That would pull horsepower up without gas mileage effect. with camshaft, valve springs, spacers, underpulleys, coil/wires and headers, u would get appx. 50 hp more. Hope the info would help u. Good luck on ur modification.