95 lumina shifting problems

I have a 95 automatic transmission lumina with around 130K on it. The problem is that at around 45 mph, the car seems to hit a lull and will not accelerate. I have to floor it and after 2 or 3 seconds, it begins to accelerate normally. The problem is also sporadic and does not seem to happen every time I drive the car. I've asked the opinion of a few mechanics, each one giving me a different answer. One guy says it could be the shift cable, another says the transmission needs to be replaced, another says I just need to get my transmission fluid flushed.

Any ideas?

If the fluid is not dark brown and acrid smelling, I'd say you have a torque converter lock up solenoid sticking. My best suggestion is to put seafoam, Lucas or trans-x trans additive and see if it frees itself up. If it doesn't within a couple hundred miles of driving, then repair is necesary. The part is cheap ($15-$20), but the labor is $$$$, as it requires the trans to be dropped for clearance.

Well, the car itself is in pretty poor shape and at this point, I just need it to last a few more months until I graduate. The problem started a while back when my girlfriend was driving it. We pulled over, I checked the fluid and found that there wasn't anything on the dipstick, just black powder. I figured that probably wasn't a good thing so we called a friend who took us to get some transmission fluid. After filling it up, its been doing this acceleration thing ever since. Would a transmission flush work? Is there any cheap solution that will get us by for a few more months?

I will look into the additive, but is that something I should use now or wait until after the transmission fluid is changed?