Sumbitch works now!
So, here is a summary of my GT500 pump installation in my 07 GT.
-Pulled original pump. Fine. Installed this pump I purchased in the classified (blow me btw.. lol). Did come with harness and second fdpm. Fuel gauge showed full till half tank,, then zero. So, I fill up the tank. Takes like 6 gallons. I figure... Suck a fart out of my ass I must have geeked up the sending unit or it is bad/damaged prior. So, take my car on a 7hr trip to get tuned on a reputable dyno/tuner. On the way just cruising on the hwy, sure as shit... ding.. 7 miles to empty when showed half just seconds before. I figure "bullshit". Keep driving.. well, for about oh... 7 MILES lol.. luckily I am 2 miles WALK to the nearest gas station (that was a cluster fuck of its own.. middle of Oklahommme). On my "nice walk" I figure the blasted siphon line to the saddle tank has come off and well, the rest of the fuel is trapped. I proceed to make the rest of the trip about 100 miles between gas stops. Tune the car all is great. I figure... to hell with it for now, I will continue my trip south (another 7 hours lol). Stopping every 100 or so miles for total 1800 mile round trip. BTW.. did you know you can only use your debit card a certain number of times per day at certain gas stations? That was fun. Anyway, I get back home to do some research (my bad for not doing this to begin with) and discover the little vertical siphon tube with the orange hat was not shipped to me by the previous owner. Well, atleast I know better now.
-Order a new piece from my man Jeremy and now "tadaa" I can go more than 100 flippin miles without filling up. Now, my damn car tells me "Dickhead" your shit is broke... DTE FLI system fault (or whatever it says exactly).
-Ok beatch,,, gloves comin off mthrfkr! I take the pumps out as carefully as humanly possible. By dumb luck when I checked the resistance.. I somehow unfucked the broken wire and the damn sending unit measured correctly. 15 on empty, 160 at full... perfect! I put the pumps back in.... "DTE FLI your shit is broke" message again and fuel gauge still reads empty.

. This time I know something stupid happened and I am stupid(er) for not finding it sooner. Sure enough. Pull pump again tonight and found the yellow wire to the sending unit was broken.. Of course, it was covered by the rubber shield and broke where the zip tie was attached by some damn gorilla. Fixed the gorilla's fuckup and VIOLA! I have a fuel gauge again!!!! "Your shit is broke" message is gone!
I'll be dipped in shit! All that, and one stupid oversite (by me). Just goes to show how valuable this forum is, and hello.. a little research and understanding of the system sure goes a long freggin way! In the future I will try not to assume I totally understand a new system right off the bat. Something that should have taken me 30 minutes ended up causing that much aggrivation.
Engineers on the fuel tanks... you can still slide your tongue across my culo!
But all in all I guess it really is not the end of the world. Beats the shit out of a mullet and camaro anyday!