The forward clutch is applied in every forward gear so I would think line pressure is good, which is what the vacuum diaphragm adjusts--boosting the pressure under high load so the clutches will grip harder. The only time the intermediate band is applied is in second gear. It's the adjustment just forward of the shift arm.
You need a 10ft# torque wrench. Back off the lock nut, tighten the adjustment screw to 10ft#. Then back off the adjustment screw 4 1/4 turns. Hold it there and torque the locknut to 40ft#.
The low-reverse band is the same procedure. It's on the other side by the modulator diapraghm.
You can also look at the servo--it's on the opposite side from the adustment screw under a cover the size of your palm held on by four screws. It's a hydraulic piston that pinches the band against the adjustment screw on the other side to squeeze a drum to a stop. It's possible the piston needs seals, but not likely. I would still look at it before pulling the tranny though. Get ready for an oil bath.
One more thing to check is that the filter isn't clogged. It takes a lot of fluid to operate the servo and maybe it's slowing it down. People also have been known to use a jack to mash the pan under the filter and restrict the pump intake.
Edit: I just re-read and noticed all shifts were bad, not just the 1-2. There's a little plug by the intermediate band adjustment. You can put a 200psi fluid gauge on it
like this one, then unhook the line from the modulator and plug it. Then attach a hand vacuum pump
like this on the modulator. Then have someone that doesn't hate you hold the brakes with the truck in gear and turn the idle up to 1,000rpm. Then with the truck in gear at that high idle, put 10" on the modulator and look at the gauge. In any forward gear it should be around 100psi. In reverse it should show about 150psi. If the pressure is low, which I think it is, the green is the worst as the longer ones give more pressure. In order from lowest to highest is Green, Blue, Orange, Black, White.
It's also worth noting that your 4.0 could have much different vacuum characteristics than the 2.8. On a 2.8 you are driving around with a lot of pedal and low vacuum since it had no power. The 4.0 is going to be driving around with a stronger vacuum signal and might be causing that lack of control pressure. I'd put a vacuum gauge on the 4.0 and see where it is when you drive around. If you are driving around at 15" instead of the 10", try to get the forward pressure to 100psi with the 15" on the hand pump instead.
EDIT 2: I found my service manual and I was correct--the 4.0 A4LD control pressure is adjusted at 15" so definately there is your problem. I would shortcut all this bullshit and try the white mod one and see if that doesn't fix it.
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i dont have email so its hard to keep up with threads unless they are fresh.
