I have been 90% disabled with IU P/T for 19 years and 2 months. I’ve just been diagnosed with Prostate cancer. Should I go for straight up total 100% or leave well enough alone?
You're already "straight up total 100%"...that's what the TDIU benefit is, a 100% total rating. However, you can add another 100% rating (prostate cancer) to that and that will likely take you to an SMC rating (housebound) that will increase your benefits. You don't have to be housebound to get the housebound benefit.
If you have the prostate cancer rated today and it gets worse in the future, you're ahead of the game. Good luck.