Hi,
Frankly, I don't think "wrong" grease is likely to be the problem, although perhaps some dirt and/or water got in there (particularly if your old boots were torn or cracked) in which case cleaning it out and then relubricating might help.
The reason I am doubting grease is the problem is just that the "correct" grease and axle grease aren't all that different. The R&P grease I use is in a tube, intended for use in a grease gun (standard stuff, also used to lube the rest of the chassis) and might be just a little thinner consistency, while the axle grease is in a can. Viscosity of both is close. About the only major difference is that the temperature rating of the axle grease is higher and I'm sure there are some additives in the axle grease to help it deal with the higher pressures of roller bearings, etc. Still, I think most axle grease I've seen would work fine in the R&P.
However, cleaning it out *might* help. But once that is done you will need to carefully work a lot of grease back in there to properly lubricate everything, before re-installing and using the R&P.
To clean, I would think you can use just about any degreaser, so long as it's fully evaporated before putting new grease back in. I'd be tempted to use "disc brake cleaner" (comes in spray cans), because it evaporates very fast and doesn't leave any residue. Use it outdoors, it's got strong fumes.
Before you start that cleaning/relubricating project, removing the R&P and such, let's clarify a few other things.
You might be able to isolate the individual steering axis at each front wheel from each other, and from the R&P. This might help pinpoint the problem and rule out some other possibilities. Just detach the tie-rod ends and steer each wheel by hand to see if each one steers reasonably freely (car should be sitting on the ground for this check). Next check if the R&P operate more freely or feels like it's binding (just turn the steering wheel). This simple test might help you decide if the binding is actually in the R&P, or in one or both of the front wheel steering axis.
Did you only work grease in through the ends while installing the new boots? Or did you also put a zerk in place of the small plug (usually brass, usually with one or more ground wires attached under it) that's atop the steering box and pump some grease into it with a grease gun, too? (If I recall correctly, five strokes with a standard grease gun is what the manual says to do, every 6000-12000 miles or so.) This is what provides the bulk of lubrication to the actual rack and pinion. There is little chance of getting grease in there through the ends of the rack tube (although the inner tie-rod ball ends certainly benefit from grease there, too.
In the recent work, did you by any chance remove the entire cap on top of the steering box (the large hex cap that has the gease zerk or plug fitting in it)? I ask because this also serves as a pinion tension adjustment and a stack of shims underneath it are used to set the amount of pressure with which the pinion bears down on the rack. If some or all those shims are omitted by accident, and the cap is replaced, the R&P will definitely tighten up a lot.
Underneath that same cap are several important parts, too. There is a cup of sorts that presses against the pinion, and a rather heavy spring. If either is worn, broken or bent, this might cause binding, too.
While the R&P is out of the car, grab the RH (passenger) side tie-rod and see if you can move it side-to-side (lateral play) in the R&P. If so, the bushing that the rack rides in, located within the tube on the RH side, is worn. It's not likely, but possible that this could cause binding or misalignment. It would certainly bind on the rack if that bushing dried out and was unlubricated by some grease.
One other thing that occurs to me, is if the outer tie-rod ends were somehow incorrectly reinstalled. Not sure if this is even possible, though. (Are the tie-rod ends greasable on your car? Lot's of the replacements available in recent years aren't greasable, are "permanently lubricated" like on most modern cars. AKAIK, only The Roadster Factory still has greasable ends available.)
Finally, have you had the car re-aligned? Incorrect toe-in, caster and camber can lead to heavy-feeling steering.
Let us know what you find.
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