Hi Randi,
I had to go through a process very similar to yours where it included 6 months of nutritionist visits and 6 months of dieting done concurrently. I am just finishing up those 6 months now while I wait for my surgery date to roll around.
You are probably going to have to have a lot of testing done between now and your surgery, in addition to the psych eval you have already had. I had to have an EKG, chest x-ray, bloodwork twice, walking pulmonary function test, and sleep study. Other people have had different testing including cardiologist and pulmonologist, etc. It all depends on your current health and the requirements of your surgeon and/or insurance.
For me the diet was and continues to be the hardest. I'm bad about going to the doctor on my own but when someone tells me to I'm pretty good about it, so it's just been a minor hassle running all over town to different labs and docs. However, the diet requires willpower, which I sometimes lack. I have fallen off the wagon lots of times, but I try not to beat myself up about it - I've had a lifetime to develop the bad eating habits and it's going to take time to change them. I just pick myself up and climb right back on that wagon (no matter how much I want to kick it sometimes) and continue on.
As you get closer to your surgery (like within the last couple of weeks) you might have to modify your diet. Some doctors require a liquid diet, some don't. You have probably already heard that getting your 70-90 grams of Protein in every day is very important - this will continue to be important after the surgery. Lots of people start trying their Protein shakes out early to see if they can find something they like. (I like unjury, myself.)
There are many more people here than just me - this is just my experience so far and everyone's experience is different. I thought I'd share mine since we both have the 6 month lead time.