Car won’t shift till 4500 rpms

I recently picked up a 2000 Le Sabre for 2k, 165k
Miles, Car had lots of throttle hesitation when i first
bought it, replaced the Throttle position sensor and
Issue was resolved perfectly, however since then
the car has been shifting out of 1st gear
consistently at 4500 RPM's Nothing more, nothing
less,

Additionally when at slow speed > 5 or so miles an
hour the car will completely die after giving it a
Small amount of gas is given (think driving through
a parking lot or drive through) However the car can
idle in park/Drive flawlessly. Really at a loss at this
point was hoping someone else had a similar
experience in the past!