Tranny going ??

I have only had this 94 Lx 4.6 for three weeks,The other day I was out driving around and the tranny acted like it just slipped into neutral,I was going about 65 mph and the RPMs at about 1800 then it jumped up to 3500 RPms.then it went back to 1800 RPMs.Even in cruise-control it was happening.So I checked the tranny fluid and it looked nice and pink,H"ave a cold and could not smell it.I went and got a bottle of lucus trans condishener(SP) That did`nt help any ay all.Now what should I do frist.My son said To have it checked out with some computer to see if it some electrical thing.The over drive lite did not come on at all ,only if I pushed the botton.

Any help would be welcome.

Tom/04 lx 4.6 98,000 miles on it.

Go to Ford or local transmission shop and have them do a diagnostic check for trouble codes. I don't think AutoZone can check for these codes but you could ask them. Have the shop flush out all of the fluid and replace the filter or do it yourself. Be sure to drain fluid out of the torque converter, also. Remove the inspection cover on the lower front of the bellhousing. Then using a breaker bar and socket on the crankshaft vibration damper bolt, rotate the engine until you see the drain plug on the front of the torque converter.