1990 535i with ZF 4HP22 automatic; 109,000 miles. Noticed this morning that the converter lockup is kind of soft; it is engaging but seems like not 100%. Used to be more firm, like a 5th shift. Had car in 'E' mode, then 'Sport' for a few miles, then switched back to 'E' when entering highway on-ramp. Mobil-1 synthetic fluid level is OK, fluid changed 7,000 miles ago and also 200 miles ago (just a drain & fill). Filter changed at 88k. My commute is 40 miles each way at ~77mph; usually runs 2,900 rpm, today ran most of the time at 2,900 but up some gradual slopes noticed rpms climb to ~3,000 to 3,100. I fear the converter clutch is slipping or is this normal? Suggestions? Any relays or fuses to check.