Sorry for the late reply, been a little busy the last few days.
Running the iron at 750 is way more than enough, I run 450 for small things and up to about 650 for big heat sinks like large power and grounds that have a lot of copper in the board to handle current. Something is wrong and the first thing I would do is use a pink pencil eraser and alcohol to clean the pads good before I tried to solder to them. If you can't get a good tin on the whole pad then it is either dirty or not enough heat is being transferred into the area of work.
Couple rules for iron longevity...
ALWAYS keep a ball of solder on the tip when not actually soldering a connection, solder is a cheap consumable and it keeps the heat from attacking the cladding on the tip and when cold protects the tip from damage if you want to clean the built up flux off the iron with a wire brush. NEVER wire brush the bare tip, if you can see any copper then the tip is toast and the cladding is gone, get a new tip.
Use a damp cellulose sponge to thermal shock the tip and clean off the old solder before applying a small amount of fresh solder to wet the tip, dry irons do not transfer heat well.
When you solder it should flow like water to all areas that are not covered with masking, when the pads and wires are properly tinned with the correct amount of solder then it is just a matter of re-flowing the 2 pieces together using just a touch of new solder (need the flux to clean the connection) or by using just flux (flux causes the impurities in the solder to come to the surface removing them from the internal area of the solder, that's how you get good shiny, strong, and electrically stable connections).