its a weird problem, my trans usually shifts real quick so i'm already in 3rd gear by maybe 30mph. but say I get into it in 1st gear but let off before it shifts to second the trans will skip second and go right to third.

Also, it doesnt really shift from 3rd to 2nd properly. I have the kickdown cable adjusted so it is tight at WOT, but when i go to WOT in third gear it doesnt shift down to 2nd all the time like I would like

Vacuum modulator? Governer? Does it have a shift kit in it? Did this just start happening, or what? A little more info. might help.

Vacuum modulator? Governer? Does it have a shift kit in it? Did this just start happening, or what? A little more info. might help.
vacuum modulator is hooked up.

the trans shifts real nice and firm so i'm assuming it has a shift kit. The bellhousing of the trans has a nice big TCI sticker on it. I bought the car with the trans in it, and it doesnt have many miles on it at all. The trans worked fine with the old mild 350 that was in there, but once i put in the 671 blown 350 with a lot more power its acting funny now

Ok, so it was working perfect before the engine swap? Shifting at the wrong time or not down shifting could be the TV cable adjustment. The "kick-down" cable is actually called the TV (throttle valve) cable. That could be the problem. You may have it adjusted too tight or too loose. I would contact TCI to get info on how to adjust it correctly.

Ok, so it was working perfect before the engine swap? Shifting at the wrong time or not down shifting could be the TV cable adjustment. The "kick-down" cable is actually called the TV (throttle valve) cable. That could be the problem. You may have it adjusted too tight or too loose. I would contact TCI to get info on how to adjust it correctly.
the 350 doesnt use a TV, it uses a detent cable that detects when WOT is acheived.

I was thinking that my problem may have something to do with boost possibly? When i get on the motor instead of the vacuum going to 0, it goes to about 7lbs of boost. Could that mess with the vacuum modulator causing it to shift funny?

Your symtoms of early change up matches with a kickdown that is to loose, not pulling up right
Check the kickdown cable where it goes into the trans, the outter cable may have pulled up when u adjusted and is stitting on the top edge of the steel sleeve going into the trans
Drop back in and readjust

Also 2x check modulator vacuum lines for leaks
Also possible faulty modulator, they are not expenisve, replace with adjustable modulator.
U may have an adjustable in there now??? have a look inside where the vac line hooks in, it will have a very small flat head screw, turn it in a couple turns, see if it makes a diff.
This will make the trans kick down noticeably with less throttle at 30 mph.

vacuum modulator is hooked up.

the trans shifts real nice and firm so i'm assuming it has a shift kit. The bellhousing of the trans has a nice big TCI sticker on it. I bought the car with the trans in it, and it doesnt have many miles on it at all. The trans worked fine with the old mild 350 that was in there, but once i put in the 671 blown 350 with a lot more power its acting funny now

I believe you are right about the boost from your 6-71 affecting your shift points. I'd recommend contacting Weiand or BDS and asking them where you take your vacuum source from for the modulator.

If the modulator Valve checks OK, I might suggest you run a Vacuum Canister and valve it to maintain 20psi and tap the modulator line to it.

I just put a new TH-350 in mine and now it's doing the same thing as yours. As Steptoe suggested try turning the screw inside the vacuum modulator in(clockwise) 2 to 3 full turns, it helped mine some. You may wind up needing a new spring in the valve body if it's worn. Did you happen to change the torque converter also? As Z15 suggested you may need to run a vacuum canister, I lost alot of vacuum with the new tranny and converter.

My thought is this - if you have a blower and tap v/m from the manifold, there isn't any vacuum because the manifold is under pressure via the blower, not a vacuum as in normally aspirated.

I believe you may have to plumb the vacuum from the carb plate, and this may not work. Otherwise, shift trans manually.

darko, I think I was wrong about your problem, and that the vacuum modulator and positive manifold pressure form the blower may be the issue. I suggest looking around on the Speed Talk sight for info. on this. Lots of good info there.