904 help

I have a 318 with a 904 that I just rebuilt. I put in a tci shift kit and Hughes converter. At first it wouldn't shift to 3rd until way too high. I have been working the kickdown cable and got it better. I noticed the other day after it sat for a few days I started it up and went to take off, but it was like there was no pressure. Or low on fluid. After revving a few times it took off and was fine. This has happened again after letting it sit. Any ideas what would cause this? Fluid is full on dipstick while running in neutral. Thanks