For 2006, GM introduced two new ECMs, E38 and E67. These controllers look somewhat similar to the E40, but slightly different connectors exist on each of the three, and none interchange. The new ECMs featured a departure from the historied 68000 series chip for a new Motorola PowerPC based 40 MHz, 32-bit RISC processor and a flash memory bumped up to a hefty 2 megabytes, or 2048 kilobytes-twice that of the replaced controllers. They are also the first GM controllers to feature floating-point processing, an improvement to the accuracy in which it makes calculations. The E67 has a slight edge on E38, thanks to its additional input/output lines, thus making it the choice for vehicles with variable valve timing. Also new for 2006 was the T43 transmission controller for six speed automatics. In another radical move, the T43 found a home 'inside' the transmission. The T43 is actually tucked in with the valve body, and has yet to receive a service part number from GM.
Clearly, GM's powertrain controllers have come a long way over the years, and we expect the ongoing evolution to continue on its advancing path. It's been 23 years since Masuoka's invention of flash memory, and 13 years since taking duty in GM's controllers. Now it's arguably one of the most important advancements that enabled the mainstream popularity of DIY custom tuning.
The Gen IV marked the introduction of a radically different looking engine control unit, drastically smaller than its predecessor. Twenty-five more terminals made there way onto the new E40 controller, for a total of 185 contacts between three connectors.... | 
...The new unit was the first that was designed to never be opened. This controller marked GM's preliminary LAN-type controller rollout. The E40 would end up being short-lived, serving only 2005 and some 2006 applications. | 
The E67 controller debuted in 2006 and appeared strikingly similar to the outgoing E40.... |