The Dow Jones Transportation Average /zigman2/quotes/210598063/realtime DJT -3.63% was chugging along in record territory Tuesday, putting them on track to trigger a fresh Dow Theory buy signal for the first time in more than five months, for all but the last two minutes of the trading day. A basic tenet of the Dow Theory is that no important bull or bear market signal could be triggered unless both the Dow transports and the Dow Jones Industrial Average /zigman2/quotes/210598065/realtime DJIA -2.53% flashed the same signal. The Dow transports rose as much as 239 points, or 1.5%, to an all-time intraday high of 16,112.87, well above the May 7 record close of 15,943.30, but a late-day pullback took it down to a 62-point, or 0.4% gain, to close at 15,936.69, or 0.04% below the record. Meanwhile, the Dow industrials closed up 16 points, or less than 0.1%, but reached a third straight record close. If the Dow transports managed to hold its gains to reach a record of its own, it would've been the first time since May 7 that the sister indexes closed at a record on the same day. And as Piper Sandler technical market strategist Craig Johnson said, a Dow transports breakout to a record close "would trigger a Dow Theory buy signal."