I used a deep well socket to remove the original switch from mine, and wound up breaking it in the process (the switch, not the socket). There was ample room to install the new switch, even though it has a fairly large can. I suppose that you could remove the filter to gain some room, but I was able to do so without removing anything but the original switch.

The harsh 1-2 shift may be due to the plastic ball in the valve body that controlls the 1-2 shift wearing. The ball will erode over time, and will cause harsh (very firm) shifts from first to second. Mine is beginning to do that and it only has 116,000 on the clock. The next time I feel like abusing myself, I will probably get it up on the lift, and drop the tranny pan, and the valve body, and replace mine. Meanwhile, I will just lighten up my right foot until i'm in second gear, and then proceed.

Bill
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Those who beat their swords into plowshares will surely plow for those who did not.