Hey there, I have a 1997 LeSabre with the 3800 series II. Its the exact same car as far as powertrain and suspension, just with different body skins. There isn't much "cheap" that you can do to a modern fuel injected car if you're looking for power upgrades that you're really going to feel. These cars were optimized pretty well from the factory. Changing the exhaust or intake is going to make more noise than cause huge power gains. I went from the factory 2.25" exhaust we have to a mandrel bent 2.5" exhaust from a 92-93 bonneville/lesabre, and am using a Thrush 20" case muffler. This increased the potential flow of the exhaust by a TON. The car seems to breathe better at higher rpms, but it doesn't really NEED much more exhaust flow than the factory setup if the engine is stock anyway. The best upgrade I have found for these engines is an Intense Racing PCM (www.intense-racing.com
). For $169 (actually it may be $169 + $50 extra since the bonneville PCMs are harder to code) the PCM will tune your engine to pull in a lot more timing when you run 93 octane (our engines are tuned for 205 hp. with only 87 octane). It will also increase the full throttle shift points up to 6000 rpms, and the PCM removes the top speed limiter.
As far as problems these cars have, the upper and lower intake gaskets are injection molded plastic with silicone O ring inserts. The lower gaskets will just about ALWAYS need to be replaced if your car has any kind of mileage on it. I just did mine as a preventative measure at 70k miles, and the lowers were melted pretty bad, allowing coolant to begin crossing over into intake passages, as well as the valley. It'* not a small job to do the gaskets since just about everything visible on top of your engine bay has to come off (alternator, ignition coils and module, fuel rails and injectors, all vac lines, etc) but a worthwhile investment to make if you plan to keep your car.
1997 was a very bad year for the 4T60E autmatic transaxle for some reason, probably due to the factory shift routines. It is very common to have chugging/shuddering under load in 3rd or 4th gear with the torque converter locked. If your transmission drives fine, say a lot of prayers and hope it keeps on going strong. I've replaced my transmission already at 70K miles.