You can spend $1,000's and maybe not correct the problem. Even brand new trucks from the factory had this problem. What happens is that the fluid bleeds down when the truck sits. It is not a pressure problem it is a bleed down problem. There is a company called RJ Machine that makes better components than Clark and once installed usually fixes it. You should be able to google their name, call them and they can tell you what you need. And no you should not do the transmission too. That sounds like bad advice to me-unless the transmission is worn out and slipping.