I have a 96 SE with 106,600 that runs great however when I am driving at 50 mph and up, shifter set for overdrive (and I believe that I am in 4th/OD) and I need to accelerate. I get a little bit of a shudder/loss of power it seems like the engine is running okay but that the problem is in the transmission.

I don't get this at any other time..like a fast start from a stop sign or jumping onto the expressway etc. It seems to me like it'* not shifting smoothly from 4 down to 3? I've tried shifting from OD to D when it happens and it seems to shift fine and not shudder.

I really only notice it happening when in OD and punching it a little...Any Ideas? I have newer plugs and wires, No throwing any SES lights/codes

Spit

Change the transmission fluid and filter and see if that doesn't take care of the issue.

Most likely that'* the 4th gear clutch shaft splines dwindling. What happens is over time they splines wear...these are small thin splines on a non-hardened part (was hardened in 2003). If the splines wear enough and you add enough power they can slip and start to fall apart, could be the shudder you feel.