1997 Chevy Blazer 4.3 vortec 4WD Weird Trans problem

97 Chevy Blazer 4.3 vortec 4wd 112,000 I have researched your sight for this problem and did not see it. So here it goes. About 50% of the time my blazer shifts absolutly fine however the other 50% is the issue. It keeps going into safe mode and staying in 3rd gear. If I shift manually to 1 or 2 it has low gear but it will not downshift or upshift on its on. This problem has been happening for about a month now and I have managed to keep track of its symtoms enough to give you this. Once it decideds to run fine it will run fine for hours. Until I turn it off! Then when restarted it may or may not run fine again. It only seems to mess up when the ignition is turned off or on. I have scanned for codes and it it giving 4. Shift circuit a falure, Shift circuit b falure, TCC Failure, and Manufacture Trans Failure. I am getting tired of being told that the only solution is a $ 2500 rebuild from all of the local shops. I am assuming that 4 problems would not appear all together. I believe it has to be one problem causing all 4 to fail. So I guess after this long winded explanation my only question is ANY IDEAS! Please for the love of everything holy ANY IDEAS.