[skorpioskorpio]

An over simplified view is that a 4L80E is essentially the TH400 design hacked to be electronic and an overdrive planetary gearset added to it's 2.48 1st ratio and 1.48 2nd ratio, 3rd is direct drive and in the 4L80 OD is .75. How you get 6 speeds is to engage the overdrive to every gear and not only to the 3rd, direct drive gear. So you get 1st, 1st+OD, 2nd, 2nd+OD, 3rd, and finally the 3rd+OD that you get normally in a 4L80. This is all done in the valve body hydraulically, and all the clutches and bands are the same as a normal 4L80. Of course you need a TCU that knows this modified valve body exists and there needs to be the supporting electronics in the trans to make it do this. PCS makes both the valve body and the controller, TCI makes a similar setup pre-assembled, however the TCI trans does not engine brake on down shifts the PCS setup does within certain rules.

Problem is that the 2.48, 1.48, 1.0, 0.75 gearing doesn't really give you 5 well spaced gears, so TCI created new 1st and 2nd planetaries with a 2.98 and 1.57 ratios which gives nice even gear spacing through the 6 possible gear ratios and increases the total gear ratio spread from a 3:1 1st through 4th to 4:1 1st through 6th. It ends up being a 6 speed trans with closer gear ratios than a stock 4 speed configuration while increasing the overall ratios bottom to top. In combination with rear end ratios it essentially gives you an extra gear on top or an extra gear on the bottom with 5 closer gears in the middle.

because the ratio drops are less, you can get the torque converter into lockup quicker, need less stall and the PCS controller will auto shift with multiple programs or go into full manual mode. So you can have a smooth touring auto shift program, a more aggessive "sport" shift program, and the manual paddle shifting. Torque converter lockup, shift points, trans pressure are all under the control of the PCS TCU and are tied to RPM and a Throttle position sensor (TPS).

There are still only 4 mechanical detents in the trans and some of the lower downshifts require a mechanical detent for engine braking though more simplistically the trans can be shifted fully electronically, it'll just freewheel on certain low gear down shifts (like all the new 6 or more gear automatics do). I was told by PCS that only 1st +OD to 1st and possibly 2nd to 1st +OD freewheel. However if these gear ratios are shifted to via mechanical means they will engine brake, so I will be using an electronic shifter that converts these shifts into mechanical events through a cable via a servo motor. The normal P-R-N-(D)-D-2-1 still needs to be present as the paddle shifter only shifts forward gears, and in my truck will be a push button + display panel for this function.

In the end I should end up with a trans that shifts, maybe not quite as fast as the double clutch exotics but way faster than you could ever shift a manual, and be in torque converter lockup almost all the time because of the low RPM drop in the closer ratios. Configured with the equivelant of a 4.11 gear rear end ratio to the "normal" 2.48 1st (which in the 6 speed would be a 3.50 rear end ratio, it puts you at 80 MPH at 2700 RPM in 6th and at 5000 rpm (way short of readline on the 4.2 which redlines at about 6500 or could be pushed to 7500+ with a different harmonic dampener) will push the truck to just shy of 150 mph, probably getting towards the limit of what a Jimmy can do aerodynamically, it is a brick afterall.