2003 Chevy Silverado 1500 starting problems

I have a 03 chevy silvereado 1500 with a 4.8L engine.  The truck has 103,000 miles.  Sometimes the truck does not start at the first turn of the key.  It will crank over about 5 times and when I release the key it continues to turn over, I will then try to start the truck again and it always fires up as it should.  I am thinking it may be a sensor but I am not sure.  I have not had a 100k tune up yet.  I don't know if that would have anything to do with this, but it seems to have started when the truck hit 100k

I am having the same problem. I'll turn the key and it'll keep cranking and cranking for about 5-7 seconds and if it starts to go, i have to rev it up some. The other problem is, i just bought it 3 days ago and it didn't do it and has no warrenty. Im at 103600 miles. Anyone know what it might be. My one friend thinks it might be that the fuel injector might be almost clogged and to put some cleaner in it. Any ideas? BTW i have a 2000 5.3 V8

It may be the classic chevy fuel pump going bad?  Once it starts does it run normal down the road?  When tackling these problems with my own vehicles I generally start on the cheap side and work up.  Check fuel pressure, change fuel filter.  It surely won't hurt to do your 100K mile maintenance but I doubt that's causing your hard starts.  When you change your plugs look them over for signs of engine system problems.  Browse the internet for pics of different looking plugs and what each one means.  Best of luck.