2005 Mercury Grand Marquis struggles to go uphill but if I
 

2005 Mercury Grand Marquis struggles to go uphill but if I turn off ignition and park for 5 minutes and then turn car back on it will go uphill no problem but this happens after about 15 minutes of driving all over again

I would check and monitor fuel pressure under those driving conditions. Check for any stored codes. Does the check engine light come on? If the engine appears to be revving up, the transmission could be slipping. Don't know with the limited information you provided.

No check engine light comes on at all it started doing it just out of the blue when I would accelerate coming off of an exit ramp and it would kind of like surge for a minute and then it would pick back up not like a slipping transmission but almost like a lack power or something and I've dealt with slipping transmissions before it doesn't feel like that

With no codes and you've eliminated the Transmission, the first suspect is fuel starvation.
Like Raski said, check the fuel pressure -- if you have a guage.
Your description indicates:
1. Clogged fuel filter -- because it starts right up and runs after sitting for a few minutes.
I would change to a Motorcraft or WIX fuel filter.
The fuel filter is located on the inside of the frame, driver's side.
1995 Grand Marquis Restoration - Mercury Forum - Mercury Enthusiasts Forums (1)

Pull the fuse/relay for the fuel pump and check for signs of overheating or corrosion. A mid level scanner should let you look at fuel pressure or splice in a fuel pressure gauge on the fuel rail. Does the fuel pressure meet specifications just idling? Take it out on the road and watch the fuel pressure..