1990 Chevy Silverado third tranny going out.

Transmission problem
1990 Chevy Silverado V8 Two Wheel Drive Automatic

ok so I bought this truck off of my cousin. When he bought this truck he had to replace the transmission. So there is number one. I bought the truck off of him and the transmission that he had put into the truck started slipping and then within a day went out. So I bought a transmission and it was already bad so that one doesnt really count but the transmission I have in it now worked great for about 3 or 4 days. Then all of the sudden the same thing that happened to the past two working transmissions happened to this one. What my dad's friend said(a transmission specialist) was that the 3-4 clutch had gone out. Is this just some sort of bad luck that im going through that all of these transmissions have a bad 3-4 clutch or is there something that could lead to this problem occurring? Ive checked to make sure the fluid runs through the cooling system and I have put a new filter and gasket in each transmission in hopes of that helping with the transmission to work. Yet the same problem has happened with each transmission. Im at a loss of thought and have no idea what to do. Should I just keep buying more transmissions or is there something else that could cause this. It is a 700r4 transmission 4speed with electronic overdrive.