2:73 to 3:42 swap

[Mike R]

I have a 1987, 2 wheel drive with a 305 tbi. Thinking about swapping the 2:73 rear end gears for  3:42s, as I hate the way my engine lugs causing the 700r4 to shift in and out of overdrive.
Will I need to reprogram my computer for the new rear end gears?
Any issues to consider other than changing the speedometer gears?

[Blazin]

That won't bother the computer at all. As you said the spedo will be off unless you swap out the gear in the tail shaft.

[bake74]

     Mike R welcome to the site from Ca.  Blazin is right on, just change out the speedo gear and all will be fine.

[bd]

Going to 3.42 may not resolve all of your nuisance downshifting.  700's are known for dropping out of O/D at around half throttle.  You'll probably need to upgrade to the Corvette 3-4 throttle valve sleeve, as well.  http://www.summitracing.com/search/?keyword=bmm-70237&dds=1

[Mike R]

Thanks to everyone for your information. As an update I took my truck to a local transmission shop the other day and the owner told me most of what I thought was shifting is in fact the torque converter locking up in both 3rd and 4th gear, possibly caused by a bad pressure switch, tps or map sensor.
I'll need to leave the truck with him for about a week before he can get to it.
I changed the tps just for the heck of it but the problem still exists, is there anything I can do myself to diagnose the problem? 

[mattgood]

Going to 3.42 may not resolve all of your nuisance downshifting.  700's are known for dropping out of O/D at around half throttle.  You'll probably need to upgrade to the Corvette 3-4 throttle valve sleeve, as well.  http://www.summitracing.com/search/?keyword=bmm-70237&dds=1

    Never seen that product before.... seems like a good idea though.