I tried both in my 67 Impala SS (4L60 with 3.31 rear gears). Started out with a custom L/U unit, stalled about 2400rpm's, rpm's at 70 were about 2200 with the TCC applied. I ran it that way for several months, then BOOM, lunched the converter and it pumped enough needle bearings thru the trans to require a complete rebuiding.
I used a ported vacuum switch/brake pedal switch/grounded on a 4th gear pressure switch deal to operate the TCC. It worked fine, unlocked at heavy/full throttle, and when coasting. I didn't really like it much, as it would "lug" the engine in 4th gear at low vehicle speeds, and clunked in and out like a factory TCC cruising around 35-50mph when we were on and off the throttle.
I replaced the L/U converter with a custom built 2400rpm with no TCC, and absolutely LOVED it. It was very well coupled for "normal" driving, and barely any rpm increase at any speed in 4th noticable over the L/U unit. Have some torque multiplication in 4th gear at lower vehicle speeds was a BIG plus over the L/U converter, which typically required enough throttle opening to unlock it to get the heavy Impala back up to speed without shifting back into 3rd. No switches, no wiring, no thumping/clunking in and out of L/U, better everyplace, IMHO.
I didn't even run a cooler with it, just in the factory replacement radiator. Ran it that way over 35,000 miles before selling the car, averaged 18-24 mpg's, and never once missed the L/U deal......FWIW.....Cliff
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https://cliffshighperformance.com/
73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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