What could I do to upgrade my truck under the hood performance wise

Keep it stock but tuned, serviced and running like it's supposed to!!!.... No matter which engine you have!... Take that money that you would waste on 'so called' performance upgrades and put it into maintenance of the truck!!.. Forget all about those 'cold air intake systems' that's a bunch of BS...and proven to be BS!!

I have a 2008 Colorado 5cyl----1st I had a cat back exaust system installed-then a K&N cold air intake-you really have to do both---when you put it in-its gotta come out and the warrantee was not affected and it runs like a bear and the mileage averages 22-25 other things like synthetic oil do really help