severe power lose at 4000 rpm

Replace the fuel filter

Fuel filter is a great starting point. Also run some high quality fuel system cleaner(I HIGHLY recommend Sea Foam) and you might want to check for a cam starting to go bad, timing set warn, weak cylinder pressure...you might just want to look at rebuilding, buying a reman, or going GM new for an engine. There probably isn't much time left in the old girl.

the power lose is exactly at 4000 rpm and is like some one flipping a switch when I let off and it shifts the power is there again and it pulls good in the next gear

That TBI engine will not have power above 4000 RPM and will actually do it best below 3500 RPM.

Ignition, distributor, computer...?

I have oowned one for 16 years and they always fall flat above 4000 RPM. You could try better gas because it is possible that you are getting into detination and it is retarding the spark and shutting it down so to speak. THere is nothing gained winding it past 4000 though because you are past its real world power peak and output is falling fast.

Good point! It is a stock SBC, not to mention VERY poor flowing intake and heads and a small CFM throttle body. I hadn't thought about that in my first reply.

Thanks guys the imformstion is greatly needed as I just got this truck running this good and am glad to find out this is normal and now I can just enjoy the life we have left together

Elderbrock makes a replacement intake manifold for that engine that flows better and will increase top end if you are interested in that. It also accepts bigger TBI units too.

Problem is the stock heads flow FAR less than the better intake.

Not that much less and a the intake is the bigger of the three choke holds on the engine. The cam is also a major factor in power curve too.

To make early TBI engines run like a small block should, cam, lifters, heads, intake, and throttle body all need to be upgraded.

True, but when the intake flows 30-40% more than the heads, you aren't gaining much. Even with an '86 or earlier set of recon heads, new stock cam(also '86 or earlier),Edelbrock intake, and Stock TBI unit with a matched set of injectors will make a WORLD of difference over the choked out weak factory TBI engine.

Not really, you will gain more than you think because there will be more air pressure availble at port to flow when valve is open. We are not talking 7000 RPM here and stock head can work well up to 5000 or a bit more with a proper cam and intake.