Remote start key fobs for 09 Sierra

Sorry if this question has been answered elsewhere, but I am new to the blog and was not able to find an answer by searching through existing posts.  I have a 2009 GMC Sierra ext cab SLE and I have confirmed that I do have RPO code AP8, so I know I have the remote start prep package and that all I need to do is buy new key fobs and have the dealer flash the computer module to enable the remote start.  However dealer is telling me I have to fork over $200 for part number 17801236.  GM's website says that part number 15913421 ($35 a piece) will work with my truck and I'm wondering why dealer is telling me I have to buy the more expensive ones.  Are 17801236 and 15913421 interchaneable and will 15913421 work with my truck?  The last eight of my VIN is 9Z231628 and I can provide full VIN if needed but dealer only asked for last 8 so I was assuming that is all that's needed.  Thanks in advance for any assistance.  

I just bought a 2009 GMC Sierra, Extended Cab, SLE w/ remote start installed.  The remote start key fob is GM Part No. 15913421 taken from the back of the fob.  I'm researching the other fob as well to see if it's available as a reasonably priced novelty.  I think the one they're trying to sell you is the one with a small LCD screen on it that gives vehicle feedback on it:  Gas Tank Level, Tire Pressure, extended start range etc.
Hope this helps.
I'd also suggest that you may find aftermarket manufacturers that can provide the fobs as well?  

Check out this site:
http://www.autotransponder.com/2009_GMC_Sierra_keys_and_Keyless_entry_remotes.php  

Hi, were you ever able to figure out if the 15913421 would work in place of the 17801236? I am looking into this also have have people telling me it will work but I would like to know for sure before I buy it?
Thanks
Joe