The ratios are about right if you also need to cruise the Interstates. Lower ratios can put you in the powerband, but I think you have to look at 4th gear engine speed at 80mph. At 80 in 4th, my engine's at 3000rpm. Regearing might bring it up another 400rpm or so which is pretty high to be holding for hundreds of Interstate miles. I think I need to check out the kickdown cable. That's probably the fix for my case.

 

hmmm.. think the TPS sensor is telling the CPU the correct throttle angle at that end of the range? That is part of the calculation for wider injector pules (mo gas please). Would show up as throttle angle % on scanner not changing beyond a certain position. Base idle is like 9%.

 

Correct. They're only for CAT performance verification. Only the two upstream sensors affect air/fuel ratio. Many have been running without downstream O2 sensors or CATs for years, including myself.

80mph is high speed for a disco. It's difficult to maintain that speed as inefficient as its aerodynamics are in addition to traveling up hill. If you want more power without gearing changes then you could add a supercharger, Tornado chip, performance cam, or 4.6 engine swap.

 

I tightened my kickdown cable and found my performance on the grade is not bad enough to indicate clogged cats.

I overadjusted the kickdown cable at first which resulted in very easy downshifts or double-downshifts (4th to 2nd) but it also caused the transmission to clunk a hard upshift almost everytime I let off the gas. So I backed it off a bit and it's working ok. The upshift clunking is noticeable only when I really cut off the gas pedal abruptly.

Paying more attention to it, I noticed the transmission isn't the smoothest but it's still comparable to a typical TH350... just not as smooth as a modern auto.

On the grade, I am getting up to 75mph now with the kickdown working. At that point I am hitting a HP limit, but I think it's making good power for what it is supposed to be, you know with the lift, roof rack and everything.

I'm not trying to go faster. I just wanted to verify my cats aren't clogged and prevent getting rear-ended by a turbo diesel when I hit a grade, fail to downshift and slow to 50! At 3 gpm of $5 premium, I'd be content to slow down if it didn't mean getting creamed.