My new problem, they seem to never go away.

This is the 90 brougham 350. When I take off from dead stop, I hear a rattling noise coming from under the hood. Its not too bad when the car is cold but when it warms up, it gets bad. My first thought is the valves need to be adjusted but now I think that a lifter may be bad. But its not a ticking sound, just a bad metal rattle on take off. The longer I drive it, the worse it gets. I spent a few hours adjusting the valves but that just left me with a big puddle of oil. What to do?

I had a similar problem but it was worse when the car was cold. For me the biggest problem was that the distributor was misaligned, so that could possibly be an issue for you as well. Does the rattling sound like a heavy knocking? If so, the pistons could be misfiring, causing the sluggish acceleration and rattling sound.
I hope this helps,

Lee

Exhaust manifold heat shields?
Cracked trans flexplate?

Valves are not throttle sensitive, if they are out of adjustment they will make noise at all throttle positions.

A metallic rattling noise sounds a lot like preignition or detonation, also known as "pinging". Is the timing stock? Try running a higher grade of gasoline and see if it changes things any. Also check that the fuel filter is clean and fuel pressure is correct. Too little fuel can cause preignition as well.

Another possibility is an exhaust leak at the exhaust manifold. Especially between the head and the manifold, an exhaust leak will make noises alot like bad valve adjustment except that tends to quiet down a bit as the engine warms up.

Apply the brake on take off see if it changes (increasing load).

Check the ignition timing, as blueeyes said, tank of premium would show a if timing is higher than it should be, OR if there is carbon buildup on the pistons/chambers, or EGR flow is restricted. EGR does NOT work when cold, typically it has to be fairly warm coolant temp to work (If I knew your ECM's broadcast code I might be able to find out specifically). GM had a lot of problems with the Olds 307's and the EGR Stack tubes getting clogged making it ping and having to run premium to save the engine from severe pinging and engine damage. Pinging is bad news.

Get some Seafoam, follow the directions on how to pour it into the carb/TBI. Not the pout into the tank, that won't cut it. OR get some GM X66P (dealer). You can use X66A also, but P is "pour", it is essentially the same stuff as Seafoam (they copied the idea). X66P is rumored to be created for Pontiac's back in the 50's or 60's when they had some problems with carbon buildup. It is old and good. Really good stuff.

Basically, pour through carb/TBI holding up to 1000-1500 rpm, until 2/3 can is poured, then dump it all in and allow engine to stall, let it sit for 15-30 min, then restart and blow it all out. Expect smoke, lots of it, a clean engine will have little smoke, a dirty one will have tons.