Brand new grill pan was seasoned but food taste rancid/metallic?
You probably used too much oil when seasoning and maybe the wrong kind of oil. When seasoning you want the thinnest layer of oil possible, and you want to season several times. I use cold-pressed flaxseed oil and season my pans five times using this method:


thoroughly clean and dry the pan. some pans (like carbon steel) come with a layer of wax to protect them from rust and this must be removed before seasoning. one manufacturer suggests cooking potato skins, salt, and oil with constant stirring for 15 minutes, then a second time to remove this. do your best to get the pan prepped properly before seasoning.
put a small amount of flaxseed oil on a paper towel and coat the entire pan, inside and out including the handle. then use a second, dry paper towel to remove the oil. there will be a very thin layer left. you want to get it as dry as possible. there will still be a micro layer of residual oil left on the pan after this step even if it seems to be too dry. it's not.
crank your oven to 550°F and let it heat up fully. then turn the pan upside down (so any oil, of which there should be none, will drip out) and leave in for an hour. then turn off the oven and let it cool compeletely.
repeat steps 2-3 five times.
depending on the pan you may want to hold off cooking eggs or things that stick easily until you have used the pan for a while. 


To answer your question of how to fix:
1. Clean your pan again using soap and steel wool and get off all your existing cooked oil. Dry thoroughly.
2. Follow seasoning steps above.