I have a 98 Tahoe 4x4 that has been having a trans issue for over year now. 1st to 2nd upshift is delayed and harsh. 2nd to 3rd seems delayed too but not as harsh on the upshift. I've done a little research and it has led me to the 1-2 accumulator spring and piston. Before I go and tear into this trans, can anyone offer me and advice on this repair? It should be straight forward but I'm concerned about all the different parts available for my truck. Rock Auto have a lot of different part numbers listed for the piston and spring(s). How do I know which one to get? Also, not sure if I am 100% right on this being the cause of the delayed and harsh upshifts but the converter has also unlocked all on it own while cruising on the highway. It only does this when its raining and it doesn't do it every time its raining. Its very strange. It will unlock and then go right back in to lockup. Its not the brake switch. I replaced the filter and fluid last summer and didnt notice anything unusual in the pan. Fluid did not look burnt. I am also running a 0411 ECM and had a buddy look at the tune and he cant see anything wrong in it. Yes, the torque management has been zeroed out but he put about 15% of it back and the shifts where still delayed and harsh. He said line pressed looked good too but I am not sure he was ale to read line pressure correctly with EFI Live.