where r some good mods to do to a 350 tbi in and out of the motor.

Change the heads or don't waste your time messing with it.

Then burn a chip (or ten) to compensate.

There is alot of stuff you can do then just changing the heads. but it will involve tuning your system to bump the timing and fuel richness at wide open throttle and other areas of running.
there is alot of info on this board but here is a link for some basic tuning info.
http://www.thirdgen.org/techboard/tbi/257455-advanced-topics-tbi-theory.html
If you do a search on the board you can find alot of usefull info.
you can shave off the lip of the tbi unit for better flow, use spacers and other ideas that are all discussed here.
I just did a tbi conversion on my truck and so far love the set up. It pulls up hills better and elevation is no longer an issue when driving in the mountains.
There are sites for getting the tunning and burning hardware and software so you can learn how to do it yourself instead of paying a hundred bucks a pop for a chip that may or may not work. That is what I am going to do pretty soon, as soon as I learn a bit more.
Another good site for tbi info is here.
http://www.binderbulletin.org/forums/forumdisplay.php?f=75
This is a good site for general knowlege and such.
Hope this helps..

There is a lot of stuff you can waste time on, but with stock heads there is no power to be had IMO.

The stock heads on TBI engines are absolutely awful.

I agree, do not buy an off the shelf chip, get yourself your own burning equipment from www.moates.net and get to burning.

There is plenty of power to tune out once you get a new set of heads on there.

Why do you say that the heads are junk, what is different about tbi heads over carb'ed?
I have never heard that and just assumed that other then valve size 350's were the same..

TBI heads have restrictive runners and poor combustion chambers, you could get your self some edelbrock heads, and intake and you can get the fueling up to par with that shit and haul ass.