So I have an 88 gl wagon with 33's on it and I want to be able to do highway speeda comfortably, does anyone know what gears I should buy?

With 33's id be more concerned about RPM loss. Taller tires means faster speed overall per RPM, meaning you could do 75 with less RPM than 75 on standard tires at "x" rpm. 

Diff ratio swap. 4.44 is the shortest you can get. Good luck fitting this to a PT4wd EA 5spd box, the pinion shaft in these gearboxes is part of the lower gearset. 

In the AWD EJ gearboxes the pinion shaft lives in a tube that the lower gearset is fitted to. 

Major mods needed. Match the rear diff to the front diff  

or just run in 3rd on the highway? 

Cheers 

Bennie

Use 3rd/4th gears.

And remember to compensate for speedometer off......you may already be going faster than you think.

I have 31"s and when my speedometer says 40, I'm doing 55, when it says 55, I'm doin 80.

It won't really push 5th gear at all.  4th I've got to be on flat-ish ground no head winds and top speed is around 65-70 (actual)

That's with a 2.2.  

Honestly spend your money on smaller tires.  33"s are too big.

With 33's you should consider an EJ swap. 

6 hours ago, wagons said:

With 33's you should consider an EJ swap. 

Not consider, DO! And not “should” either. Nike  

Cheers 

Bennie