With this many miles I would assume the tranny is shot. Your clutches are probably burnt, crispy, and about to totally disintegrate. First, check your fluid, not so much the level; you want to see the color and the smell. If it is dark and has a burnt smell, just get it rebuilt. Make sure they put in a new pcs, a sonnax tcc regulator valve, and a new boost valve. The fourth clutch hub loves to strip out the spline too. The front sun gear and the final drive sun gear love to pit on the tooth face.
These are the week points in you tranny. With a good reputable shop doing the work, you should be all set.
97 Bonneville SSE
01 Bonneville SE
95 Bonneville SE