I'm don't have any big gear, so your setup is a bit out of my area of expertise. But a 5.0 on a 130 litre board sounds like you're pushing the boundaries a bit.
If the sail is too small for the board it can have a tendency to steer the board downwind (this is common for people trying to teach their kids with small sails on bigger boards).
A great way to make up ground is to use the swell or waves (even small stuff) when coming back in towards shore. Once you feel the board pick up the ride of the swell you can get the board pointed a lot higher than you normally could. It sometimes helps to come out of the straps and stand more forward on the board to do this.
Some good advice from some of the others on here.
Look for others out in the water who are making ground up wind and see if you can find things they seem to be doing different than you... foot position, sail position, body position etc, etc, etc
Have fun. I've been at it for 30 years and still learning... and love it!