Buffalo - in February? Unless you have a heated garage, this isn't a real good time to lay the flooring!
But it sounds like you are determined to get it done.
Bite the bullet and do this or you'll be stuggling for months - and you will need a heat gun or forget it until summer:
Pull the bench seat completely out.
Remove the sills, kick panels and any boot/trim for the trans case.
Here's the tough part - remove your new floor covering.
Bundle it up and take it into the warmest place you can find. Lay it out as it will sit in the truck and let it relax. Take a couple of 1 gallon paint cans and use them under the flooring to simulate the hump.
In the meantime get the floor of the truck wicked clean - vacuum and wipe down with acetone (or gasoline). In addition to the heat gun, get a can of spray adhesive (3M 77 is good) and a rubber mallet.
When you have nothing left but a clean steel floor and a warm carpet (and a warm sunny day if possible) lay the covering down again.
Center it on the hump, push it back into the rise for the seats. Using the heat gun on a medium setting, warm the carpet down the hump and where it tee's out along the seat risers.
When it is flexible enough from the heat gun, take the rubber mallet and bang it into the contours of the hump and risers. Always be using your hands to smooth it out.
When you have this middle part shaped to the contours of the steel floor, fold the carpet back and tack it in place with the adhesive.
After you have that center hump/seat rise area moulded and tacked down, the rest should flow out easily.
Using the heat gun, work from the middle and smooth the cover out. Always pushing any lumps down. Working up the towards the firewall rise and out to the sills.
Another area that is hard to shape is along the sides of the seats - use the plenty of heat and pound the covering into the contours.
As areas start to conform to your satisfction, flip the carpet back and tack it down with the 3M 77.
Good luck. This job is way easier in the summer but it can be done in the cold.
Also, dont stress too much about lumps. Given enough time and foot traffic, they will eventually lay down and smooth out.
