PSX freezes when saving Civ 2

hey I have the scph-7501, old grey model, psx, bought it from a game
shop few yeard back, in perfect condition.
playing civilization 2, on large world, with 7 opponents, and rather
far along in the game, 1946, with lots of tech, and can see the whole
earth now. it takes about 5 minutes for a turn to process at this
point.
game play is smooth, the activision movie at start is mostly smooth
with smooth sound, only hiccups once or twice for a fraction of a
second. the intro plays well also, barely jerky every few seconds. this
is about as good as I can ever remeber this being on anyone's psx.
is this also everyone elses experience?
i can play any other game I have with no problems.
the only problem i have here is saving. i can load my game easy enough.
if I do nothing and save it is ok. if I change a couple things and save
it is ok. but if I end turn and just ok through everything, then save
the first chance I get, it just hangs, and nothing seems to do any
good.
I've tried tapping the console, i've tried playing it on every side,
and upside down. I've opened it up and cleaned everything out.
i've read some places that say the old model psx had some cache issues,
and I'm wondering if this is what I am experiencing, or if it is
something else? anyway how to fix it? is there someway to
increase/improve the cache/memory, if that is my issue?
since civ 2 is one of the most popular games I figure someone has to
hav had this problem. or with any other game that takes lots of memory.
10 blocks to save. and yes it is a Sony mem card, and I've tried it in
both slots.
all these yeaers I have never finished the game on a large world. on
medium and small sure, no prob. i seem to recall this saving was always
an issue on a large world far along in the game. i want some way to
save so I can finally say I beat the large world on a hard level.
thanks anyone
James