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16-Speed: More Gears Than You Can Shake Three Sticks At

By Jerrod Jones | Photography: Jerrod Jones
I once drove a K5 Blazer from the bottom of the country to Idaho and back. I did so with 39-inch tires, a 500 HP big-block, three transmission speeds, no climate control, no top, earplugs, and a very loud stereo. The blazer got an amazing 12 miles per gallon at 70 MPH and I was happy the entire trip, rain or shine.
While I enjoyed the trip immensely then – and am in no way admitting to having softened up – I feel like I might not take pleasure in that same trip now. I’m going to blame it on the current price of fuel. Although, it may also have something to do with the 3,000 rpm my engine was spinning on the freeway and the ringing in my ears that stayed with me for months after the last trip. The three-speed TH400 transmission, combined with 4.88 gears, kept the big-block at a healthy roar through four states, and “fuel sipping” is not a term I’d use to describe a big-block with three speeds behind it. Of course, I wanted an overdrive gear.
Years later, after constant abuse and airtime, the back of the TH400 housing broke off completely. There is little doubt that the 240 pounds of my iron NP203/NP205 dual transfer case setup helped that happen – even with its own second crossmember – but the strength and multiple gear ratios convinced me to leave it in place.
The best way to improve my K5’s performance, fuel economy, and drivability: add gears and lose pounds. The TH400 and NP203/NP205 doubler combination had served me well, but the 1-ton non-overdrive transmission combined with two iron transfer cases was weighing in on the high side of heavyweights.
While I could have just gone and bought a newer 4 x 4 for the cost of the parts I was about to install, I instead dropped in the “Ferrari of drivetrains” and obtained what I really wanted from the very beginning: a Gearstar 4L80E overdrive transmission combined with Advance Adapters’ Atlas four-speed transfer case. The package equates to 16 speeds of power management that ended up dropping 100 pounds off the back of the transmission and improving fuel economy with the addition of a 0.75 overdrive gear. The combination was so close in size to the original TH400/ NP203/NP205 grouping that we did not even have to change driveshaft lengths. The only downside (and why I didn’t do this in the first place) is the cost. At around $7,500, it’s not a cheap slush-box-and-T-case combo. Adding on, you’ll also need a brain like HGM’s CompuShift II to manage the electronically controlled 4L8-E transmission – something that tacks on an additional $1,000.
Can I justify the cost of parts in fuel savings? Certainly not. And I would never try to. But, I can justify the expense with driver happiness and improved performance in the vehicle. On top of that, the new transmission and transfer case are completely fresh and will allow me many more thousands of (enjoyable) miles before needing a rebuild.